After rebuking Peter for his change in conduct (vv.11-14), Paul now expands and explains.
“We are Jews by birth and not Gentile sinners, yet we know that no one is justified by the works of the law but by the faithfulness of Jesus Christ. And we have come to believe in Christ Jesus, so that we may be justified by the faithfulness of Christ and not by the works of the law, because by the works of the law no one will be justified”.
Some think that this is a further part of Paul’s rebuke of Peter, but, whether it is or not Paul now makes the point that even though he and Peter and all other Jews are Jews by birth, they know that no one is justified by the works of the law but by the faithfulness of Jesus Christ.
Paul seems to be transitioning here from defending himself, his ministry, and his teaching to defending his other major tenet: justification by faith.
Here in v.16 he uses this word, “justification”, for the first time. It’s a legal word, borrowed from the courts of law of the day. It means that the person in question has been “declared righteous” and has been absolved of the potential consequences of the crime they are supposed to have committed. Paul writes that nobody can work their way to this point (no one is justified by the works of the law) and that there is only one way to stand before God and be viewed as righteous and absolved of the potential consequences of sin (by the faithfulness of Jesus Christ).
The same point that Paul is making to the churches in Galatia is true for you too. The system we see in the Old Testament of law-keeping in order to be justified in the sight of a holy and righteous God will never work. Burdening yourself with the task of earning and deserving your justification is a fruitless and winless task (v.16). Instead, Paul is teaching (and we now are accepting) that people should believe in Jesus Christ and this will be counted to them as righteousness (cf. Genesis 15.6).
I would really encourage you today to stop and evaluate what you are doing with your time, your talents, and your tithe (your finances). Are you using them in a vain attempt to prove to God how good you are and how much you deserve to be acquitted of the consequences of your sin? Are you binding yourself with works of law?
Or, as you ought to be, are you using your time, your talents, and your tithe in such a way that demonstrates your utter gratitude for having been justified by the faithfulness of Jesus Christ? One is a fruitless and winless task, one is the clear teaching of the Word of God.