Romans 3:2

Much in every way! First of all, they have been entrusted with the very words of God.

(v2, NIV)

So what advantage has the Jew? Their advantage is in the fact that they were given the law. This they have been given is God's words. What a privilege it is to be entrusted with such a thing. So, it is advantageous to be a Jew for this very fact. Most devout Jews know the law inside out. They can quote it to you and they live in it and breathe in it. To be a Jew and be born into a culture where that is promoted is quite an advantage. As Paul was saying in the last chapter, they had the law but their circumcision was being undone by the breaking of the law. So, you can have the law but it doesn't mean that you follow what it says. Regardless, to be a Jew and to have been entrusted with the words of God is a valued advantage. This advantage is not to be cast aside as something useless or meaningless.