Since the grace of God toward sinful mankind is not absolute, or arbitrary, but mediate (in Christ Jesus, Rom. 3, 24), the redemption of our Savior constitutes its indispensable foundation, 1 Cor. 3, 11.
The doctrine of Christ (Christology) therefore follows logically upon that of divine grace as the cardinal article of the Christian faith, with which the Church stands or falls (articulus stantis et cadentis ecclesiae). While usually this expression is applied to the doctrine of justification, and rightly so, we must not forget that without the vicarious satisfaction of Christ there could be no doctrine of justification by grace, through faith. Hence, as the redeeming work of our Lord is the foundation of the doctrine of divine grace, so it is the foundation also of the doctrine of justification. This becomes evident when we consider that faith justifies only as trust in Christ as the divine Redeemer, who died for our sins (Matt. 16, 13-17; 1 Tim. 2, 6: ἀντίλυτρον ὑπὲρ πάντων) and not as trust in Him as a new "Teacher of ethics," or as a "perfect Ideal," or as a "great Revealer'' of the "fatherhood of God," and the like. In view of this fact the paramount importance of the doctrine of Christ is obvious.
The doctrine of Christ is commonly treated under three heads :
The assumption that the Son of God would have become incarnate even if man had not fallen into sin must be rejected as a useless, yes, dangerous speculation. It is useless, since human reason without divine revelation can never discover what God would have done had man not destroyed his happiness by sinning. It is dangerous, not only because it involves a basic element of pantheism, but also because it ignores the only purpose of Christ's. incarnation which Scripture mentions, namely, the salvation of lost and condemned mankind, Matt. 18, 11; 1 Tim. 1, 15; Gal. 4, 5_ Augustine: Si homo non periisset, Filius Hominis non venisset.