Galatians 2:15-16

"We who are Jews by birth and not 'Gentile sinners'

(v15, NIV)

Apparently Paul lists a distinction here between Jews and Gentiles. Gentiles are labelled as sinners. Paul knows that everyone is a sinner, but perhaps he is labelling it here in accordance with the view that is common among Jews.

know that a man is not justified by observing the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by observing the law, because by observing the law no one will be justified.

(v16, NIV)

These Jews who are distinguished between Gentile sinners know that justification does not come from observing the law. If they do not know, then they should know that at least. He is probably not speaking simply to Jews, but Jews who have come to accept the gospel of Christ. This fact Paul is speaking about is true and he could address everyone about it, but the Jews were the ones that had this particular problem. They had become legalists in their thinking and have veered from the truth of the gospel.

The only way to be justified is to be justified by faith in Christ. Putting your faith in Christ is exactly what Paul does.

For it is by grace you have been saved, through faith - and this not from yourselves, it is the gift of God - not by works, so that no one can boast.

(Ephesians 2:8-9, NIV)

Now, this doesn't mean that works aren't important.

For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.

(Ephesians 2:10, ESV)

This follows Ephesians 2:8-9, highlighting that we are created for good works.

So also faith by itself, if it does not have works, is dead.

(James 2:17, ESV)

Even though we are saved by grace through faith, it's dead without works.

For it is not the hearers of the law who are righteous before God, for the doers of the law who will be justified.

(Romans 2:13, ESV)

Notice that it is not the doing of the law that justifies. However, only those who are doers of the law will be justified. I heard a sermon on this and maybe I'll relay that information on another post someday.