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 fullness of the times of the adoption had arrived, that the kingdom of heaven had drawn near, and that He was dwelling within those that believe in Him who was born Emmanuel of the Virgin. To this effect they testify, [saying,] that before Joseph had come together with Mary, while she therefore remained in virginity, “she was found with child of the Holy Ghost;” and that the angel Gabriel said unto her, “The Holy Ghost shall come upon you, and the power of the Highest shall overshadow you; therefore also that holy thing which shall be born of you shall be called the Son of God;” and that the angel said to Joseph in a dream, “Now this was done, that it might be fulfilled which was spoken by Isaiah the prophet, Behold, a virgin shall be with child.” But the elders have thus interpreted what Esaias said: “And the Lord, moreover, said unto Ahaz, Ask for yourself a sign from the Lord your God out of the depth below, or from the height above. And Ahaz said, I will not ask, and I will not tempt the Lord. And he said, It is not a small thing for you to weary men; and how does the Lord weary them? Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son; and you shall call His name Emmanuel. Butter and honey shall He eat: before He knows or chooses out things that are evil, He shall exchange them for what is good; for before the child knows good or evil, He shall not consent to evil, that He may choose that which is good.” Carefully, then, has the Holy Ghost pointed out, by what has been said, His birth from a virgin, and His essence, that He is God (for the name Emmanuel indicates this). And He shows that He is a man, when He says, “Butter and honey shall He eat;” and in that He terms Him a child also, [in saying,] “before He knows good and evil;” for these are all the tokens of a human infant. But that He “will not consent to evil, that He may choose that which is good,”— this is proper to God; that by the fact, that He shall eat butter and honey, we should not understand that He is a mere man only, nor, on the other hand, from the name Emmanuel, should suspect Him to be God without flesh.
Source: Adversus haereses (New Advent)