We know that a person is not justified by works of the law but through faith in Jesus Christ. Galatians 2:16

In order to understand this text fully, you need to read the context:

11 But when Cephas came to Antioch, I opposed him to his face, because he stood condemned. 12 For before certain men came from James, he was eating with the Gentiles; but when they came he drew back and separated himself, fearing the circumcision party. 13 And the rest of the Jews acted hypocritically along with him, so that even Barnabas was led astray by their hypocrisy. 14 But when I saw that their conduct was not in step with the truth of the gospel, I said to Cephas before them all, “If you, though a Jew, live like a Gentile and not like a Jew, how can you force the Gentiles to live like Jews?”

15 We ourselves are Jews by birth and not Gentile sinners; 16 yet we know that a person is not justified by works of the law but through faith in Jesus Christ, so we also have believed in Christ Jesus, in order to be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified.

17 But if, in our endeavor to be justified in Christ, we too were found to be sinners, is Christ then a servant of sin? Certainly not! 18 For if I rebuild what I tore down, I prove myself to be a transgressor. 19 For through the law I died to the law, so that I might live to God. 20 I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. 21 I do not nullify the grace of God, for if righteousness were through the law, then Christ died for no purpose.

• You have probably heard people say things such as, “I hope this good deed will make up to God for some of the bad things I used to do.” Or they say, “I think God owes me something after all the things I have put up with.” They are expressing the belief that their behavior determines God’s attitude toward them. What does this verse say in response to such ideas?
• Almost everyone has at some time or other done something that feels so good that it deserves God’s favor. When did you feel that way? What does this verse say to your feeling?
• Have you ever broken one of the Ten Commandments? Did you do it on purpose fully recognizing you were doing wrong, or did you do it thinking the situation completely justified your behavior? If the situation seemed to justify the behavior, why was the behavior wrong? Is God unreasonable? Would it be better to think as secularists think, that the situation, not some dusty old law, determines what is right and wrong?
• If you can’t earn heaven by your behavior, why should you behave?
• In Ephesians 6:16, Paul wrote, “Take the shield of faith, with which you will be able to quench all the flaming arrows of the evil one.” How can you use your faith in Christ as a shield against evil?