Justification by faith alone (sola fide), apart from our works, was a guiding principle of the Reformation. Ultimately, however, the Reformers emphasized justification by faith alone because they wanted to guard the truth that we are declared righteous before God because of Christ alone (solus Christus). Faith, we will see, is the means by which we receive the righteousness of Christ and not, properly speaking, what actually secures our justification. We must have faith in Christ to be justified, but faith is not the righteousness that avails before God’s judgment. Only the obedience of Christ can do that.
We have seen that the law of God, though it was not given to sinners as a covenant of works or as a means by which to secure one’s own righteousness, nevertheless holds out the promise of justification for all who keep it perfectly (Rom. 2:13). We have also seen that God’s original covenant with humanity was one wherein Adam would have earned eternal life for himself and his progeny if he had perfectly obeyed God (Gen. 2:15–17; Rom. 5:12–21). These truths tell us something very important: God demands complete obedience. Keeping His commandments halfway or even most of the way is not enough to meet His judicial standard. And since our Creator is fully just, He cannot simply change His demands when they are not met. After the fall, God gave sacrifices to His people so that they could maintain fellowship with Him as they continued to fall short of His perfect standard. But the Lord never relaxed His demand for perfection. From a legal standpoint, God still demands that we be perfect (Matt. 5:48).
But we have also seen that because of sin, not because of any flaw in God’s law, this standard is impossible for us to meet. So, in His grace, God chose a different way to give us the perfect obedience we need to stand before Him. He chose to accept the obedience of another in place of our own. This is what Paul tells us in today’s passage. “By the one man’s obedience the many will be made righteous” (Rom. 5:19). Paul is looking at all of Christ’s obedience from birth to death as a whole, and he is speaking of righteousness in a forensic or legal sense. The flawless obedience of our Savior is what constitutes us as righteous or what provides the basis for God’s declaring His people righteous. Dr. R.C. Sproul writes in his commentary Romans: “The question is not whether we are going to be saved through works; the question is whose works. We are saved through the works of the one who alone fulfilled the terms of the covenant of works.”