Behold. — An interesting case of a corrupt reading which has found its way into the Authorised version. For “behold,” a decisive consensus of the best MSS. has “but if.” The corruption was very obvious and easy. Adopting “but if,” the answering clause of the sentence is to be found in the question, “Teachest thou not thyself?” Romans 2:21. The connecting particle “therefore” at the beginning of the same verse is merely resumptive, or, as it is technically called, “epanaleptic.”
Turning to the Jew, the Apostle breaks out into indignant and vehement apostrophe, “If you have the name of Jew, and repose upon the Law, and make your boast in God, and do all these other things — why then, while you profess to teach others, do you not teach yourself?” A fine specimen of the natural eloquence which the Apostle derives from intense feeling. The different features of the picture crowd into his mind to point the contrast between what the Jew claimed to be and what he was.
Restest in. — Reposest or reliest upon a law. A passive confidence in something external. “In the Law the Jew saw the Magna Charta which gave him his assurance of salvation” (Meyer).
Makest thy boast of God — i.e., of a peculiar and exclusive claim to His favour. (Comp. Deuteronomy 4:7; Psalms 147:19-20.)