Some of the Jews may claim circumcision as advantage, but in the end, the Jews still fell short of the law. Then Paul asks rhetorically the advantage if the Jew has circumcision (3:1). The short answer is that they don't (and even if they did, they still couldn't fully meet God's standards).
In fact, Paul writes that "to [the Jews] were committed the oracles of God" (3:2). In other words, the Jews had access to God's standards (i.e.: Ten Commandments). But that means that they would be held to a higher accountability because they know the law -- many of them can't just use ignorance as an excuse!
So in the end, both Jews and Gentiles (and basically all of us) are unable to match God's standards, and even the things the Jews have ultimately don't help them in matching God's standards. But a few verses later, Paul will tell them of something, really someone, who DOES match God standards on behalf of us.