3:15 is accomplished with greater clarity and detail. The simple way to grasp this is to say that the Old Testament is the story of God’s promise and the New Testament is God’s fulfillment of all he has promised. One of the crucial ways the Bible moves from promise to fulfillment is by using typology. This is an unusual word, and it’s a word we don’t use in everyday conversation. But it’s a biblical word, and its meaning isn’t difficult to grasp.