It's not that Paul's saying that being a Jew who follows Jewish law and is circumcised is not a big deal, because it totally is. It's great actually! Twenty points to the children of Israel!
Paul tells us that the Jews were the first people God shared his wisdom and laws with, so he knows they're cool in the Big Guy's eyes.
Sure, it's true that some Jewish people have been unfaithful to God over the years. For example: there are all those Jews who still stubbornly refused to believe Jesus is the messiah. (Not cool, according to Paul.)
But everyone lies. Everyone sins. No one really knows God. Way to bring us down, Paul.The good news is this doesn't make any difference to God. The crappiness of the world just reveals how awesome God actually is. Sweet.
Again, Paul stresses that Jews and Gentiles are on the same footing. No one gets a head start in the race to salvation.
This is basically because God sent Jesus to save everyone in the entire world. Only he can help us stop being so sinful and jerky all the time.
Yes, Paul says, Jewish law tells us what sin is and that's super important. (So, don't chuck out those Torahs just yet, guys.)
But the most important thing now is that God has sent Jesus. This is the natural continuation of Jewish law, but it's also outside of it. Whoa, Paul's blowing our minds.
Look, basically, God is going to save everyone who believes in Jesus no matter what their background was before they came to believe. Everyone sins. That means everyone needs Jesus. It's pretty simple.
God did all this for us because he's a totally forgiving guy. He essentially just erased all our previous sins from his heavenly ledger and decided to give us a do-over. Now we're square with him again.
The word Paul uses to describe this over and over again is we're now "justified."
So really the big take-away here is that no one should go around bragging and shouting from the rooftops that they have some special access to God. God gives everyone access to him through Jesus. Everyone. Now don't you feel silly up there on that rooftop?