Audio commentary on this verse

Note 7 at Ro 10:19: What was it that Israel knew? Paul was saying that Israel knew the Gospel of salvation by faith, which he had expounded on in this epistle. One way this truth was revealed in the Old Testament was through the prophecies concerning the Gentiles becoming the people of God. If God was going to embrace nationalities that didn't adhere to the rites and ceremonies that were delivered to the Jews, then it should have been evident that these things were not prerequisites to salvation.

Paul quoted a prophecy from Moses and two additional passages from Isaiah to verify that this truth was revealed in the Old Testament. The truth was there, but the Jewish hearts had become so hardened through legalism that they couldn't perceive this truth (see note 3 at Mr 8:17).