In Luke 17:7-10, Jesus talked about a slave and his master. After his day of work, the slave was expected to prepare a meal, then eat after the master. Furthermore, the master was not expected to thank the slave for accomplishing his assigned tasks. It was simply his duty. Jesus applied this relationship to his disciples, saying, “So you too, when you do all the things which are commanded you, say, ‘We are unworthy slaves; we have done only that which we ought to have done.’” Based on Romans 3-4, all the saved should utter the same sentiment.
Romans 4:1-8 discusses Abraham and the righteousness credited to him by God because of his faith. His faith (his belief in God’s promises and his works of obedience) caused God to credit righteousness to him. Abraham’s faith did not earn him righteousness. Abraham was still guilty of sin and could have rightly said of himself, “I am an unworthy slave before God; I have done only that which I should have done.” But because of his faith, God gave righteousness to him. According to Romans 3:21-26, that righteousness is the great gift given through Jesus’ death to all who have faith like Abraham’s.
No amount of obedience can erase sins. But without obedience, there is no faith, according to Romans 1:5 and James 2:17. Obedience is required for faith to be genuine, but even genuine faith cannot remove sin to make one worthy or righteous in the sight of God. For any sinful person to become righteous before God, Jesus’ sacrifice must be applied to their account. Then righteousness is credited to you as it was to Abraham. And when all that is done, you should say, “I am an unworthy slave; I have done only that which I ought to have done.” As Paul said in Romans 3:27, “Where then is boasting? It is excluded. By what kind of law? Of works? No, but by a law of faith.”