Exchange No. 3 is the gracious, unmerited, indeed demerited, exchange that God provides in Christ. Without compromise of His righteousness revealed in wrath, God righteously justifies sinners through the redemption He provides in Christ—the blood-propitiation for our sins. This Paul states in the rich and tightly packed words of Romans 3:21–26.
It is only later in the letter that he gives us a different, and in some ways more fundamental, way of looking at this. There he says that the Son of God took our nature (coming “in the likeness of sinful flesh,” Rom. 8:3) in order to exchange places with Adam, so that His obedience and righteousness might for our sakes be exchanged for Adam’s (and our) disobedience and sin (Rom. 5:12–21).
Exchange No. 4 is that which is offered to sinners in the Gospel: righteousness and justification instead of unrighteousness and condemnation. This Christ-shaped righteousness is constituted by His entire life of obedience and His wrath-embracing sacrifice on the cross, where He was made a sin offering (coming “on account of sin,” Rom. 8:3).
In addition to Paul’s four-fold insistence on the fact that this divine exchange is consistent with the absolute righteousness of God (3:21, 22, 25, 26), he stresses that this way of salvation is consistent with the teaching of the Old Testament (“being witnessed by the Law and the Prophets,” 3:21, cf. 1:1). He also insists that we contribute nothing to our salvation; it is all “of grace.” The sheer genius of the divine strategy is simply breathtaking.
Exchange No. 5 emerges here. In John Calvin’s movement in his Institutes of the Christian Religion from Book II (on the work of Christ) to Book III (on the application of redemption), he writes: “We must now examine this question. How do we receive those benefits which the Father bestowed on His only-begotten Son not for Christ’s own private use, but that He might enrich poor and needy men? First, we must understand that as long as Christ remains outside of us, and we are separated from Him, all that He has suffered and done for the salvation of the human race remains useless and of no value to us … we obtain this by faith” (Institutes, III. i. 1, emphasis added).
In response to the great exchange that has been accomplished for us in Christ, there is an exchange accomplished in us by the Spirit: unbelief gives way to faith, rebellion is exchanged for trust.
Paul expresses himself at this point with meticulous precision. Justification is always said to be “by faith,” never “on account of/on the basis of faith.” Faith is not the ground or basis upon which we are justified, but the means or the “instrument.” Our faith is in Christ, in whom our justification, our “right-wising” with God, has been accomplished. In Archbishop William Temple’s oft-quoted words: “All is of God; the only thing of my very own which I contribute to my redemption is the sin from which I need to be redeemed.”
This is clear enough in what Paul says in his basic exposition. It is made even clearer in his application of that exposition in Romans 3:27–30. Here he argues that all boasting in relationship to justification is excluded. But then he probes the question of why. He asks, “By what law [i.e. principle]? Of works? No, but by the law of faith.”