ectypal.net

Further, as long as Christ is outside of us and we are out of Christ, we can receive no fruit from another’s righteousness. God willed to unite us to Christ by a twofold bond—one natural, the other mystical—in virtue of which both our evils might be transferred to Christ and the blessings of Christ pass over to us and become ours. The former is the communion of nature by the incarnation. By this, Christ, having assumed our flesh, became our brother and true Goel and could receive our sins upon himself and have the right to redeem us. The latter is the communion of grace by mediation. By this, having been made by God a surety for us and given to us for a head, he can communicate to us his righteousness and all his benefits. Hence it happens that as he was made of God sin for us by the imputation of our sins, so in turn we are made the righteousness of God in him by the imputation of his obedience (2 Cor. 5:21).