Paul continues his line of thought from last week, where he was telling the Jews why being a Jew is a great advantage and benefit when it comes to the gospel. After heling the Jewish part of his audience to see the gospel through a uniquely Jewish lens, he's back to the earlier issue of their sense of superiority. He anticipates the question in his readers doubling back to that issue... "So, you're saying we are better than the Gentiles now?"
And you can imagine Paul, like a person being interviewed on television and being misunderstood and misrepresented by the questioner, trying to impose their own idea on what he's saying, Paul is steadily addresing each progression of thought... and here, it's like he's staring into our hearts, going, "No, that's still not what I'm saying."
And he summarizes again, that both Jews and Greeks are under sin, guilty, deserving of God's judgement and in need of God's grace. He then quotes different parts of the OT to confirm in his own day and for every day what was true in the past, that there is nobody that can stand before God on their own merit or righteousness. All of us are sinners, having removed God from his throne, in our own minds and hearts, committing cosmic treason against him and trying to diminish his glory for our own self-enhancement.
Paul's point is that this game we play of comparing ourselves to each other, as if we can be right before God because I'm better in some sense than my neighbor in my own assessment. We tear others down and puff our chests out as if this impresses or fools God. But, it's a silly and stupid game. It's a sinful game in itself. The reality of sin and guilt in every one of us has levelled the playing field. We have no high horse on which to sit and elevate ourselves over anyone. There is no room for pride and arrogance and superiority in Christianity because the first principle of Christianity is your guilty and isnful and worthy of judgement and only the mercy and grace of a perfect substitute can make peace with God. If any of us stands right before God it is only because we've abandoned self-reliance in favor of faith in Christ's righteousness. So, there is no room for us to boast outwardly or even to feel superior inwardly. Christ is the only thing we have to boast in.
This is so important for us to understand and to return to again and again, because everything in us drifts toward pride. We war against that by letting the gospel bring us low in our own hearts continually, so that we might receive and abide in grace, which is the grounds of our salvation and sanctification.
We have only Jesus to appeal to. Nothing and no one else.