13 But that both the apostles and their disciples thus taught as the Church preaches, and thus teaching were perfected, wherefore also they were called away to that which is perfect— Stephen, teaching these truths, when he was yet on earth, saw the glory of God, and Jesus on His right hand, and exclaimed, “Behold, I see the heavens opened, and the Son of man standing on the right hand of God.” These words he said, and was stoned; and thus did he fulfil the perfect doctrine, copying in every respect the Leader of martyrdom, and praying for those who were slaying him, in these words: “Lord, lay not this sin to their charge.”
Thus were they perfected who knew one and the same God, who from beginning to end was present with mankind in the various dispensations; as the prophet Hosea declares: “I have filled up visions, and used similitudes by the hands of the prophets.” Those, therefore, who delivered up their souls to death for Christ's Gospel— how could they have spoken to men in accordance with old-established opinion? If this had been the course adopted by them, they should not have suffered; but inasmuch as they did preach things contrary to those persons who did not assent to the truth, for that reason they suffered.
It is evident, therefore, that they did not relinquish the truth, but with all boldness preached to the Jews and Greeks. To the Jews, indeed, [they proclaimed] that the Jesus who was crucified by them was the Son of God, the Judge of quick and dead, and that He has received from His Father an eternal kingdom in Israel, as I have pointed out; but to the Greeks they preached one God, who made all things, and Jesus Christ His Son.
Source: Adversus haereses (New Advent)