As we have discussed in previous studies, the idea of fulfillment in the New Testament does not mean an annulment of what came before in the old covenant. It has to do instead with the truest achievement or expression of what was revealed in the Old Testament (Matt. 5:17–20). For example, when Matthew refers to Jesus as the Son of God whom the Father calls out of Egypt (2:13–15), the apostle is not saying that Jesus completely nullifies every sense in which Israel is His son, the sonship of Israel being the original emphasis of the passage Matthew quotes (Hos. 11:1). Instead, Matthew is teaching us that Jesus is the fullest, the most robust expression of God’s son, Israel, because He alone followed His Father’s will perfectly and accomplished Israel’s vocation of being a light to the nations (Isa. 42:6).
New covenant fulfillments make crystal clear what was latent in the old covenant revelation, as we see in today’s passage. After a lengthy session wherein he uses Psalm 95 to encourage the new covenant community to persevere (Heb. 3:7–4:11), the author of Hebrews reminds his audience of the power of the Word of God. It is like a sword that penetrates to the depths of our being, body and soul (vv. 12–13). There is no getting away from Scripture; it will have its way with its hearers whether or not they like it. It will expose the true intention of the heart, either by drawing people to hear and do its message or in abandoning sinners to the hardness of their hearts so that they fall away. The inner attitude of each of its hearers will be revealed according to how he or she responds to the Word of God.
We can speak of this teaching on sacred Scripture as being a fulfillment of the old covenant view of the Word of God in that the author of Hebrews leaves us without any doubt as to the efficacy of Scripture. Under the old covenant, the people of God were told that the Word accomplishes the purpose for which it is sent (Isa. 55:10–11). Hebrews 4:12–13 makes clear what that purpose is — to create faith in some and evoke resistance in others. Scripture can do this because it is God-breathed, and so is always accompanied by the power of the Spirit to accomplish the Lord’s intent (2 Tim. 3:16–17; Rev. 2:1–7). John Calvin comments on today’s passage, “God never speaks in vain; he draws some to salvation, others he drives to ruin.”