“Paul proclaims Christ as the fulfillment of the promise of God to Abraham, as the seed in which all the families of the earth shall be blessed (Gal. 3:8, 16, 29), the eschatological bringer of salvation whose all-embracing significance must be understood in the light of prophecy (Rom. 15:9-12), the fulfillment of God’s redemptive counsel concerning the whole world and its future.
This redemptive-historical significance of Paul’s Christology also comes to light in the pronouncements, so characteristic of him, concerning Christ as the revelation of the mystery.
Here the past is not described only as a time of darkness and ignorance, but rather as the preparation of the work of God in the course of the centuries.
The grace that has now been revealed ‘was given in Christ Jesus long ages ago’ (2 Tim. 1:9), in the purpose and promise of God and in their initial realization; it was promised by God who cannot lie, before times eternal (Tit. 1:2).
Therefore the mystery that has been revealed with the advent of Christ must also be made known and understood ‘by means of the prophetic writings’ (Rom. 16:26).
The nature of that which has taken place in Christ becomes clear in the light of the fulfilling action of God how much the Old Testament is the book of Christ (2 Cor. 3:14; 1 Cor. 10:4; Gal. 3:16).
For this reason one of the leading motifs of Paul’s preaching is that his gospel is according to the Scriptures (Rom. 1:17; 3:28; cf. Rom. 4; Gal. 3:6ff; Gal. 4:21ff; 1 Cor. 1-10; Rom. 15:4; 1 Cor. 9:10; 2 Tim. 3:16).
However this use of the Old Testament by Paul is further to be judged in detail, a most basic conception of Christ’s advent and work lies at the root of this whole appeal and use, that of the divine drama being realized and fulfilled in His advent and work; this fulfillment was not only foretold by the prophets, but signifies the execution of the divine plan of salvation that He purposed to Himself with respect to the course of the ages and the end of the times (Eph. 1:9, 10; 3:11).
This is the fundamental redemptive-historical and all-embracing character of Paul’s preaching of Christ.”
–Herman Ridderbos, Paul: An Outline of His Theology (Grand Rapids: Eerdmans, 1966/1975), 51.