Isaias 7:11

4. For the one and the same Spirit of God, who proclaimed by the prophets what and of what sort the advent of the Lord should be, did by these elders give a just interpretation of what had been truly prophesied; and He did Himself, by the apostles, announce that the fulness of the times of the adoption had arrived, that the kingdom of heaven had drawn nigh, and that He was dwelling within those that believe on Him who was born Emmanuel of the Virgin. …

6. But what Isaiah said, “From the height above, or from the depth beneath,” was meant to indicate, that “He who descended was the same also who ascended.” But in this that he said, “The Lord Himself shall give you a sign,” he declared an unlooked-for thing with regard to His generation, which could have been accomplished in no other way than by God the Lord of all, God Himself giving a sign in the house of David. For what great thing or what sign should have been in this, that a young woman conceiving by a man should bring forth, a thing which happens to all women that produce offspring? But since an unlooked-for salvation was to be provided for men through the help of God, so also was the unlooked-for birth from a virgin accomplished; God giving this sign, but man not working it out.

XI. But for the time that remains, my most attentive hearers, let us take up the old man, the receiver of God, and our pious teacher, who hath put in here, as it were, in safety from that virginal sea, and let us refresh him, both satisfied as to his divine longing, and conveying to us this most blessed theology; and let us ourselves follow out the rest of our discourse, directing our course unerringly with reference to our prescribed end, and that under the guidance of God the Almighty, so shall we not be found altogether unfruitful and unprofitable as to what is required of us. …

Now, to this point we have come in our discourse, because of the Pharisees and Sadducees coming together unto Jesus, who disagreed in matters relating to the resurrection, but came, as it were, to an agreement for the sake of tempting our Saviour, and asking Him to show them a sign from heaven. For, not satisfied with the wonderful signs shown among the people in the healing of all forms of disease and sickness, and with the rest of the miracles which our Saviour had done in the knowledge of many, they wished Him to show to them also a sign from heaven. And I conjecture that they suspected that the signs upon earth might possibly not be of God; for they did not hesitate indeed to say, “Jesus casts out demons by Beelzebub the prince of the demons;” and it seemed to them that a sign from heaven could not spring from Beelzebub or any other wicked power. …

22. But the Jews say again, This was said to Ahaz in reference to Hezekiah. Well, then, let us read the Scripture: Ask thee a sign of the Lord thy God, in the depth or in the height . And the sign certainly must be something astonishing. For the water from the rock was a sign, the sea divided, the sun turning back, and the like. But in what I am going to mention there is still more manifest refutation of the Jews. (I know that I am speaking at much length, and that my hearers are wearied: but bear with the fulness of my statements, because it is for Christ’s sake these questions are moved, and they concern no ordinary matters.) Now as Isaiah spoke this in the reign of Ahaz, and Ahaz reigned only sixteen years, and the prophecy was spoken to him within these years, the objection of the Jews is refuted by the fact that the succeeding king, Hezekiah, son of Ahaz, was twenty-five years old w …

231. “This generation,” it says, “is an evil generation. It seeketh a sign, and there shall no sign be given it, but the sign of Jonas the prophet.” A sign of the Godhead then is not given, but only of the Incarnation. Thus when about to speak of the Incarnation the prophet says: “Ask thee a sign.” And when the king had said: “I will not ask, neither will I tempt the Lord,” the answer was: “Behold a Virgin shall conceive.” Therefore we cannot see a sign of the Godhead, and do we seek a measure of it? Alas! woe is me! we impiously dare to discuss Him, to Whom we cannot worthily pray!