Reading the New Testament might seem much more manageable than reading the Old Testament. However, if you don’t read the Old Testament (or read it as it ought to be read), you might be missing out on further riches in your New Testament reading. Why is this the case? I have space for only one reason, so I’ll pick the obvious one: the New Testament records the fulfillment of the Old Testament and thus displays God’s faithfulness to his promises.
If you want to understand the depth of the New Testament, you need to understand what it fulfills, namely, the content and types found in the Old Testament, which provide a basis of understanding for the New Testament. In other words, the New Testament continues to develop the themes, topics, and storyline of the Old Testament. If we are to make sense of the New Testament, we must know the Old Testament.
Once one begins to understand, for example, the promises of the Christ and the Abrahamic and Davidic covenants in the Old Testament, he or she will be blown away at the opening of the Gospel of Matthew: “Jesus Christ, the son of David, the son of Abraham” (Matt 1:1). If one does not know the promises of the Messiah (the Christ), David’s Son, and if one does not know the blessing of Abraham to the world (Gen 12:1–3), the fact that Jesus is this promised offspring might mean very little to you when it really has global and universal significance. Or, likewise, when Jesus says, “The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel” (Mark 1:15), we will not comprehend what a momentous time has dawned.
As such, one principle for reading the New Testament that correlates to reading the Old Testament is to read the New Testament as a book of fulfillment. This means that when we read the New Testament, we ought to be thinking how it relates to the Old Testament. Most fundamentally, we ought to be thinking of how the New Testament continues, develops, and builds upon the story of salvation in the Old Testament, and how it contains many fulfillments of Old Testament promises.