Romans 3:27-30

“Where is boasting then? It is excluded. By what law? Of works? No: but by the law of faith.
Therefore we conclude that a man is justified by faith without the deeds of the law. Is He the God of the Jews only? And not also of the Gentiles? Yes, of the Gentiles also, since there is one God, who shall justify the circumcision by faith, and the uncircumcision through faith.”

Indeed, if all men are proven to be sinful, and every individual of us guilty before God of violating His righteous law, how does anyone have anything of which to boast? Indeed, anyone with a requirement for propitiation is excluded from boasting, for whatever ‘good’ he  might claim to his credit is sullied by the wrong he has committed.

So then, pitiful men must fall upon the grace and mercy of a loving God or suffer the remedy of justice for our own sins. If only by His grace do we escape wrath, of what do we have to brag?