Romans 4:2

We know that he obtained justification. If that justification had been earned by his own works it would then have been something to be proud of; it would be a pride that he might fairly hold both towards men and towards God; for to men he could point to the privileged position that he had gained, and in the sight of God he would be able to plead a certain merit of his own. But he has not this merit. His justification was not earned, but it was bestowed upon him, not for the sake of his works, but of his faith. This is the express statement of Scripture. And hence it follows that though his privileged position in the sight of men remains, he has nothing to boast of before God.

But not before God. — This is an instance of the rapid and eager dialectic of the Apostle. If the whole train of thought had been given it would probably have run much as above, but the greater part of it is suppressed, and the Apostle strikes straight at the one point which he intended to bring into relief. (Whatever there might be before men) there is no boasting before God.