“For if righteousness were through the law, then Christ died for no purpose” (Gal 2:21).
John Calvin, from his commentary on Galatians, writes,
Hence it follows, that we are justified by his grace, and, therefore, not by works… If we could produce a righteousness of our own, then Christ has suffered in vain; for the intention of his sufferings was to procure it for us, and what need was there that a work which we could accomplish for ourselves should be obtained from another? If the death of Christ be our redemption, then we were captives; if it be satisfaction, we were debtors; if it be atonement, we were guilty; if it be cleansing, we were unclean. On the contrary, he who ascribes to works his sanctification, pardon, atonement, righteousness, or deliverance, makes void the death of Christ.
Martin Luther, from his commentary, says:
Is it true that Christ suffered death or not? Did he suffer in vain or not? Unless we are quite mad, we have to answer that he did indeed suffer, not in vain or for himself, but for us… Take the…law, which contains the most perfect religion and the highest service to God — that is, faith, the fear of God, the love of God, and the love of our neighbor — and show me anyone who has been justified by it. It will then be true that Christ died in vain, for anyone who is justified by the law has power to obtain righteousness by himself… If you grant this, it must follow that Christ died in vain… Are we to allow this horrible blasphemy that the divine Majesty, not sparing his own dear Son, but giving him up to death for us all, should not do all these things seriously but as a sort of joke? I would rather see all the saints and holy angels thrown into hell with the devil. My eyes will see only this inestimable price, my Lord and Savior Christ.