Isaiah 7:13

(Verse 13.) And he said, hear therefore, house of David: Is it not enough for you to be troublesome to men, that you are also troublesome to my God? Who is this that said, hear therefore, house of David? Not God who had said above to Ahaz: Ask a sign for yourself from the Lord your God; but a Prophet, as is proven from what follows: For you are troublesome to my God. And the meaning is: because you not only persecute the prophets and despise their words; but you also contradict the present and commanding judgment of God; so that you bring upon yourself the labor, as he says in another place: I have labored, enduring (Isaiah 1:14), therefore the Lord will do what follows. Regarding the labor and trouble that Aquila and Symmachus have translated, LXX and Theodotius have interpreted it as a struggle and contest, because the contentious ones do not submit their necks to the Lord's service, but with Him willing to heal their wounds, they reject healing. And it should be noted that when the impious King Ahaz did not want to seek a sign, the prophetic message should be directed to the house of David, that is, to the royal tribe mentioned above: And they reported these things to the house of David, saying: Syria and Ephraim have joined forces.

And when He says, "Hear, O house of David," [Isaiah 7:13] He performed the part of one indicating that He whom God promised David that He would raise up from the fruit of his belly (ventris) an eternal King, is the same who was born of the Virgin, herself of the lineage of David. For on this account also, He promised that the King should be "of the fruit of his belly," which was the appropriate [term to use with respect] to a virgin conceiving, and not "of the fruit of his loins," nor "of the fruit of his reins," which expression is appropriate to a generating man, and a woman conceiving by a man. In this promise, therefore, the Scripture excluded all virile influence; yet it certainly is not mentioned that He who was born was not from the will of man. But it has fixed and established "the fruit of the belly," that it might declare the generation of Him who should be [born] from the Virgin, as Elisabeth testified when filled with the Holy Ghost, saying to Mary, "Blessed art thou among women, and blessed is the fruit of thy belly;" [Luke 1:42] the Holy Ghost pointing out to those willing to hear, that the promise which God had made, of raising up a King from the fruit of [David's] belly, was fulfilled in the birth from the Virgin, that is, from Mary. Let those, therefore, who alter the passage of Isaiah thus, "Behold, a young woman shall conceive," and who will have Him to be Joseph's son, also alter the form of the promise which was given to David, when God promised him to raise up, from the fruit of his belly, the horn of Christ the King. But they did not understand, otherwise they would have presumed to alter even this passage also.