The church has employed two terms in speaking of the eternal Son’s relation of origin. This, however, does not mean that one can distinguish the Son from the other divine persons by two ways; rather, there are two manners of talking about the same/one mode of subsisting whereby the Son is distinguished. These two manners of speaking refer to “the idea of procession and the concept of eternal generation” wherein eternal generation is one of the divine processions, particularly, that of the Father-Son relation. In regards to the former term, according to Aquinas’ Trinitarian theology, “the term procession applies to the origin of the Son and of the Holy Spirit,” however, “procession designates, more precisely the origin of the Holy Spirit.” Thus, the term “generation” has been considered more precise although both terms refer to the same thing, that is, the origin of the eternal Son. Allen will even say, “the notion of procession is expanded, even if not entirely clarified, by the idea of eternal generation.”
These two terms do not refer to the outer works of God (opera Dei ad extra). The eternal generation of the Son is an immanent action; that is, an opus Dei ad intra—inner work of God. Now the phrase, “origin of the Son,” refers to the Son as being from and equal to the Father. This is seen in creedal language: “God of God, Light of Light,” or from the term, “homoousios,” that is, of the same substance (consubstantiality). To understand the eternal generation of the Son, we will first expound this doctrine, that is, explain what eternal generation refers to; second, we will explain this doctrine by way of negation; third, we will give a biblical defense of this doctrine; and finally, we will then explain the distinctive, personal property of the Son.
Preliminary Note: Clarification and a Statement of Finitude
Before expounding this doctrine, we must first confess that we finite creatures are in the realm of the ectypal attempting to understand the archetype. Francis Turretin says, “here (if anywhere) we must be wise with sobriety so that content with the fact … we should not anxiously busy our thoughts with defining or even searching into the mode (which is altogether incomprehensible), but leave it to God who alone most perfectly knows himself.” Turretin’s humble reminder does not stand by itself. In fact, this is but an echo of those who preceded him. Some of which have said: “the begetting of God must be honoured by silence;” and, “the knowledge of the mystery of his generation is more than I can attain to—the mind fails, the voice is dumb.” God truly is ineffable—and so is the eternal generation of the Son.
Here, one may question if forming a doctrine of eternal generation is going too far into rabid speculation of that which is transcendent. However, Scripture aids man and we really are, with redeemed intelligence awakened by the Spirit, enabled to think of such ineffable things. While analogy is there, this doctrine is not driven by phenomenological (creaturely experienced) analogies as an earthly father in time begets his finite child. In fact, “we will not get very far if we ‘regard God the Father in the begetting of his only begotten Son as being similar to any human being or other animal in the act of begetting.’” In talking of the Son’s eternal generation one must remember “‘God is not as man,’ Athanasius says in this regard; we need, therefore, to ensure that language about God is not constrained by the ‘rule of human generation; or by the rule of human infirmity.’”
If this is so incomprehensible, one may ask, why attempt to understand it? If this can be drawn from analogy, but “we will not get very far” in drawing analogies, why pursue deeper knowledge of the ineffable? Is this not dangerous speculation wherein we may trample or tame God’s transcendence? These questions are daunting and only one reply can suffice: the Scriptures, which are for our contemplation, speak of the Son’s eternal generation. While the analogy is surely there, the doctrine of the Son’s eternal generation, and therefore our knowledge and pursuit of better and humble understanding of it, can only be drawn from the Scriptures wherein direct reflection can turn to dogmatic deduction. Disagreement here exists as we will later discuss in brief. Again, this is in the realm of finite knowledge as we must humbly confess. Now, one note must be given before proceeding concerning everything written henceforth. In Webster’s words: “Adverting to the incomprehensibility of the Son’s generation from the Father is not a merely formal or conventional gesture; it is meant in earnest, and places brackets around everything that follows.”
The Doctrine of Eternal Generation
To begin, we shall present a simple understanding of the Son’s generation; then, we can go into further exposition. The generation of the Son refers to the Father’s communication of the one indivisible essence to the Son. As Webster puts it: “Eternal generation is the personal and eternal act of God the Father whereby he is the origin of the personal subsistence of God the Son, so communicating to the Son the one undivided essence.” In other words, this work of the Father whereby he communicates the one, indivisible essence, which he possesses, to the Son is the Son’s origin and consequently, the Son is thus like that of the Father. Because the Son possesses or subsists in this indivisible essence, which the Father does also and communicates to the Son, he is thus perfectly equal to the Father in every respect. Turretin helps us in this regard. He says, “this wonderful generation is rightly expressed as a communication of essence from the Father (by which the Son possesses indivisibly the same essence with him and is [thus] perfectly like him).” In fact, the Son is so identical with the Father, that he too spirates (breathes out) the Spirit together with the Father.
To give a drastically over simplified description of what eternal generation connotes about the Son could go as follows: eternal generation refers to the Son as the exact representation of the Father wherein the Son is the Son from/of the Father as the one ever-flowing from and only from the Father. Here, the Son is identical to the Father in regards to essence, but is distinguished from the Father by way of relation: the Father begets the Son and is thus father to the Son, whereas the Son is from the Father and is thus Son from and of the Father.
Many things here, however, may be taken wrong. To further our limited understanding of the Son’s generation, we have decided to speak of it via negativa—by way of negation. That is, by speaking of what the Son’s eternal generation is not so that we can begin to better understand what it is.
The Eternality of the Son’s Generation: “Begotten, Not Made”
The Son’s generation, that is, the Father’s begetting of the Son, is not a “making” wherein the Son comes into existence as a creation/creature. We confess with the church that the Son “is begotten, not made.” While Turretin’s definition recently given above is incredibly helpful, the language of “made perfectly like him,” is perhaps misleading or at least has baggage. The Son’s generation is not a coming into being. There is not a genesis to the Son (or any person of the Godhead for that matter[!]). God’s essence truly is simple, a se (from and in himself), and therefore, immutable and fully complete and perfect (actus purus).
A coming into being refers to a deficiency and thus this deficiency implies a lack of something, which is contrary to aseity and pure actuality. Further, it implies potency (i.e., changeability), which is contrary to immutability. Since the Son is identical to the Father in regards to the indivisible essence that the Father truly communicates to him, the Son really is perfect just like the Father. Thus, the Son, with reference to his essence, is simple, a se, immutable, and therefore, the Son has no potential because he fully is. This means that the Son cannot be made or more particularly, his generation cannot be said to be a “coming into being” or a creation. This is so because simplicity, aseity, and immutability (and actus purus) consequently leads to or implies eternality. These incommunicable attributes help us understand and know that the Son’s generation is not act of making or a coming into being or becoming actualized.
Because God is actus purus (fully actualized/realized), he has no potential—he has nothing to change. He is immutable. This means that God is “Complete and perfect in himself … [he] has no potential that is already fully realized … there is literally nothing for God to become.” Horton’s phrase, “there is literally nothing for God to become,” is grounded in the fact that God already is. Since God is, he must always be who he is for any and every change would diminish his being. If God changed, he would no longer be who he is. Therefore, if there was any change in God, he could not say, “I AM WHO I AM,” but he in fact does say this (Exod 3:14). As Bavinck puts it, “If God were not immutable, he would not be God. [God’s] name is ‘being,’ and this name is ‘an unalterable name.’ All that changes ceases to be what it was. But true being belongs to him who does not change. That which truly is remains.” In other words, immutability requires infinitude and thus eternality. Bavinck rightly says, then, “God is not a process of becoming but an eternal being.” Or, as Calvin said, “he is self-existent and therefore eternal.”
The essence of God helps one better understand the Son’s generation. Since the Father communicates the self-existent essence to the Son and thus the Son subsists in the undivided (simple) essence, the Son’s mode of subsisting in this undivided essence must be eternal because the divine essence is unchangeable and eternal. Remember, God is simple. This means that persons and essence are inseparable. To revisit the concept of person, a person is the divine essence subsisting in a proper manner. Since the divine essence is eternal and unchangeable and since this essence is inseparable to the persons, a personal mode of subsisting must be unchangeable and eternal.
This means that to speak of the Son’s generation is not to speak of antiquity; rather, it is to speak of an ongoing, continual, more precisely, an eternal act wherein the Son is eternally the Son from the Father. The Son’s generation is not temporary. The Father did not enjoy some form without the Son. As Allen says, “The Son is not generated after some interval of solitary existence enjoyed only by the Father; no, the Son proceeds eternally and spontaneously from the Father.” The generation of the Son then is not a coming into being (contra Arianism). Rather, it is the mode whereby the Son is the Son eternally from and only from the Father. With this in mind, then God the Son subsists in the very same essence that the Father does. Therefore, the Son is consubstantial, homoousios, with the Father—he is equally divine.
A Biblical Defense of the Doctrine of Eternal Generation
Some contemporary theologians either question, critique, or even reject the notion of the Son’s generation stating that it is either unhelpful or far-fetched. In doing so, they replace eternal generation with, for example, divine obedience for the distinguishing property of the Son. Bruce Ware along with Wayne Grudem seem appear to run along these lines. However, we, along with the majority of church history, affirm the eternal generation of the Son, taking it to indeed be a biblical doctrine. For a biblical defense of this doctrine, due to space, we will turn to one primary text: John 5:26.
According to Don Carson, John 5:26 makes the notion of the Son’s eternal generation as “unobjectionable.” In this text, Jesus says, “For as the Father has life in himself, so he has granted the Son also to have life in himself” (Jn 5:26). In this we see a couple things. First, God the Father possesses (ἔχει; echei) aseity—life in himself—and thus he subsists in the divine essence, in which he absolutely exists. Second, the Son also possesses aseity (again, life in himself) as the Father has life in himself. Hence, both persons are thus fully and equally God.
But there is more to this, remember, “equality does not require sameness.” A distinction is made: the Father grants (ἔδωκεν; edōken) the Son to have aseity. Given the semantic range of δίδωμι (didōmi), one can read this as “the Father gives aseity” to the Son. This granting/giving is the communication of aseity—that which can only be attributed to the divine essence—to the Son, hence the notion of eternal generation: the Son is equal to and yet distinct from the Father whereby the Father communicates the undivided essence to the Son. This clear distinction in equality helps us identify the distinctive personal property of the Son.
The Personal Property of the Son
In the attempt to identify the personal property of the Son, one may try to ascribe two: spiration or eternal generation, for since the Son is thus perfectly like the Father as one eternally generated by him, he too breaths out the Spirit. However, because spiration can be attributed to multiple persons, it cannot be a personal property of the Father or Son; rather, it characterizes persons denoting activity or passivity. Therefore, the distinctive personal property of the Son is filiation/generation (sonship). He and he alone experiences eternal filiation/generation (sonship)—the receiving of all of who he is—from and only from the Father. As such, he is Son from the Father wherein he is Son of the Father. We can ascribe this as the personal property of the Son because he alone in the Godhead is only from the Father—it is what distinguishes him from the other two. Thus, filiation is not something common to the Father or the Spirit, but rather, it is that which is proper to and only proper to the Son. The Son is not the Father or the Spirit, but he is Son of the Father. Therefore, the name, “Son,” is not only fitting, but also proper to the second person of the Trinity.
Summary of the Son
God the Son is the eternal begotten one of the Father, eternally equal to the Father with reference to essence. The Son’s personal property is filiation/generation—one who is Son of the Father whereby he is eternally from and only from the Father with respect to relation of origin. This relation consists of the Father eternally communicating to the Son the undivided, divine essence wherein the Son receives from the Father, and is thus like the Father. This relation is eternal, that is, without beginning or end. Therefore, the Son is not a creature, that is, he is not made; instead, he is eternally begotten—one who is Son of the Father. Finally, that which distinguishes the Son from the Father and the Spirit is that he is only from the Father as the eternal begotten one, that is, his distinctive personal property is filiation/generation.
Here, one might wonder if this is abstracting too far away from the created realm. Further, one might question how this has any relevance to Jesus Christ and his saving mission. Space here forbids a thorough defense and rationale of why this is important, but two brief note shall suffice. From the words of John Webster:
 Far from abstracting from the history of the economy [i.e., created realm], theological talk of the relations of origin is a way articulating the infinite depth within the being of God, that ocean whose tide is the missions of the Son and the Spirit by which lost creatures are redeemed and perfected.
 The only historical Jesus there is is the one who has his being in union with the Son of God who is eternally begotten of the Father. Those who pore over the gospels searching for another Jesus (whether their motives be apologetic or critical) pierce hearts with many pangs, for they study a matter which does not exist.
In short, talk of these relations of origin help us better understand the depth of our salvation because it is this one who is eternally from the Father who becomes incarnate, being sent from the Father, and perfectly lives in our stead and bears our punishment on the cross.
 R. Michael Allen, Justification and the Gospel: Understanding the Contexts and Controversies (Grand Rapids: Baker, 2013), 86. The former term here would only distinguish the origin of the Son from the Spirit by the Son’s proceeding from only one other person.
 Gilles Emery, The Trinitarian Theology of St Thomas Aquinas trans. Francesca Aran Murphy (New York: Oxford University Press, 2007), 52. Emphasis original.
 Allen, Justification and the Gospel, 86.
 Francis Turretin, Institutes of Elenctic Theology 3 vols. trans. George Musgrave Giger, ed. James T. Dennison, Jr. (Phillipsburg, NJ: P&R, 1992), 1:302.
 Gregory of Nazianzus, Third Theological Oration, XXIX.8 quoted in John Webster, God Without Measure: Working Paper in Christian Theology vol I. God and the Works of God (London: Bloomsbury T&T Clark, 2016), 1:31.
 Ambrose, On the Christian Faith (NPNF 2.10), I.x.64 quoted in Webster, God Without Measure, 1:31–32.
 Webster, God Without Measure, 1:32, Webster quotes Origen, On First Principles, G. W. Butterworth, ed. (New York: Harper & Row, 1966), I.2.4.
 Webster, God Without Measure, 1:32, Webster first quotes Athanasius, Against the Arians, II.35, and then quotes Ambrose, On the Christian Faith, I.x.66, I.xi.71.
 Allen, Justification and the Gospel, 87–88.
 Webster, God Without Measure, 1:32. Emphasis added.
 Ibid., 1:30.
 Turretin, Institutes of Elenctic Theology, 1:292–293. Brackets replace the word “made” to bring clarity to any confusion of the Son being “made,” which is discussed in the next section.
 Ibid., 1:293.
 Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims On the Way (Grand Rapids: Zondervan, 2011), 235.
 Since the phrase, “אֶֽהְיֶ֖ה אֲשֶׁ֣ר אֶֽהְיֶ֑ה” (I AM WHO I AM), is in the imperfect tense, it can be translated in the future tense denoting eternal duration (see John Calvin, Calvin’s Commentaries: Harmony of Exodus Leviticus Numbers Deuteronomy vol. II trans. Charles William Bingham [Grand Rapids: Baker Book House Company, 2003], 73).
 Herman Bavinck, Reformed Dogmatics, 2:154. Emphasis original.
 Thomas Aquinas, Summa Theologiæ, 1a.8.1.
 Bavinck, Reformed Dogmatics, 2:163.
 Calvin, Calvin’s Commentaries: Harmony of Exodus Leviticus Numbers Deuteronomy vol. II trans. Charles William Bingham (Grand Rapids: Baker Book House Company, 2003), 73.
 Webster, God Without Measure, 1:87.
 Allen, Justification and the Gospel, 87.
 For example, see Grudem, Sytematic Theology, 248–252 and appendix 6; Bruce Ware, Father, Son, and Holy Spirit: Relationships, Roles, and Relevance (Wheaton, IL: Crossway, 2005), esp. 69–71.
 D. A. Carson, The Gospel according to John, PNTC (Grand Rapids: Eerdmans 1991), 257.
 Allen, Justification and the Gospel, 78.
 For a helpful discussion on this text, see Webster, God without Measure, 1:25.
 Webster, God Without Measure, 1:41.