As a monk, Luther was greatly troubled by a deep sense of guilt from his sin. He knew he fell far short of what God required in His moral law as set forth in the Ten Commandments. He further discovered that neither confession, fasting, pilgrimage, nor the pursuit of piety gave him any relief. It was only when he came across these words in the Bible written by the Apostle Paul, “The just shall live by faith” (Romans 1:17), that he saw hope.
Through that verse, he finally came to understand and believe that his sins were forgiven by faith in the person and work of Jesus Christ, apart from any works of his own. Luther came to see that Jesus Christ, God in the flesh, had come to do for him what he could not do for himself. But what does that mean?
Firstly, God requires absolute perfect obedience to His Law, but “all have sinned and fall short of the glory of God” (Romans 3:23). Further, the Bible teaches that, “there is none righteous, no, not one… there is none who does good, no, not one” (verses 10, 12).
But Jesus Christ came to keep all the requirements of God’s Law on behalf of the believer. Jesus Himself said, “Do not think that I came to destroy the Law or the Prophets, I did not come to destroy but to fulfill” (Matthew 5:17). Therefore, no good deeds or works need be or can be added to Christ’s completed obedience.
Further, God’s justice requires disobedience of His Law to be punished, but no man could ever pay the infinite debt due to God for His sins. Jesus Christ took upon Himself all of the sins of believers as if they were His. He then went to the cross and suffered the full penalty for those sins. That sacrifice of Himself was once for all. After His resurrection, He ascended bodily into heaven and will remain there until He returns bodily at His second coming. He never needs to be sacrificed again, and the believer never needs to be punished for his sins because God’s demand for justice has been fully satisfied in Christ.
The Apostle Paul summed this all up when he wrote, “He (the Father) made Him (Christ) who knew no sin to be sin for us, that we might become the righteousness of God in Him” (2 Corinthians 5:21). Luther came to see and believe this, and called it a “marvelous exchange”. By faith alone, his debt for his sin was paid in full and the obedience of Christ was considered by God to be as if Luther had fully obeyed. In this way, Luther became fully justified before God.
After God had used the verse, “The just shall live by faith” to bring about Luther’s conversion, Luther wrote, “Night and day I pondered until I saw the connection between the justice of God and the statement that ‘the just shall live by his faith’. Then I grasped that the justice of God is that righteousness by which through grace and sheer mercy God justifies us through faith. Thereupon I felt myself to be reborn and to have gone through open doors to paradise. The whole Scripture took on a new meaning, and whereas before the ‘justice of God’ had filled me with hate, now it became to me inexpressibly sweet in greater love. This passage of Paul became to me a gate to heaven…”
But if the believer is fully pardoned and therefore justified before God, what motivation is there for ongoing obedience to God and good works? Luther saw his justification as the greatest motivation, not for earning any merit, but for obeying and doing good works out of profound gratitude, joy and love for God for saving him who was so undeserving and so helplessly lost in his sin. It is no wonder that John Newton would later write, “Amazing grace! - How sweet the sound - that saved a wretch like me!”