Romans 4:2

For if Abraham were justified by works - The Jew proceeds: - I conclude, therefore, that Abraham was justified by works, or by his obedience to this law of circumcision; and, consequently, he has cause for glorying, καυχημα, to exult in something which he has done to entitle him to these blessings. Now, it is evident that he has this glorying, and consequently that he was justified by works.

Apostle. But not before God - These seem to be the apostle's words, and contain the beginning of his answer to the arguments of the Jew, as if he had said: - Allowing that Abraham might glory in being called from heathenish darkness into such marvellous light, and exult in the privileges which God had granted to him; yet this glorying was not before God as a reason why those privileges should be granted; the glorying itself being a consequence of these very privileges.

For if Abraham ... - This is the answer of the apostle. If Abraham was justified on the ground of his own merits, he would have reason to boast, or to claim praise. He might regard himself as the author of it, and take the praise to himself; see Romans 4:4. The inquiry, therefore, was, whether in the account of the justification of Abraham, there was to be found any such statement of a reason for self-confidence and boasting.

But not before God - In the sight of God. That is, in his recorded judgment, he had no ground of boasting on account of works. To show this, the apostle appeals at once to the Scriptures, to show that there was no such record as that Abraham could boast that he was justified by his works. As God judges right in all cases, so it follows that Abraham had no just ground of boasting, and of course that he was not justified by his own works. The sense of this verse is well expressed by Calvin. "If Abraham was justified by his works, he might boast of his own merits. But he has no ground of boasting before God. Therefore he was not justified by works."

4:2 The meaning is, If Abraham had been justified by works, he would have had room to glory. But he had not room to glory. Therefore he was not justified by works.