Jerome
Catena Aurea · Matthäusevangelium 1
Now all this was done, that it might be fulfilled which was spoken of the Lord by the prophet, saying, Behold, a Virgin shall be with child, and shall bring forth a Son, and they shall call His Name Emmanuel, which being interpreted is, God with us. Here we must enquire why he should say all this was done, when above he has only related the conception. It should be known that he says this to shew, that in the presence of God all this was done before it was done among men. Or he says, all this was done, because he is relating past events; for when he wrote, it was all done.
(ubi sup.) What is spoken to Ahaz then is to be thus understood. This Child, that shall be born of a Virgin of the house of David, shall now be called Emmanuel, that is, God with us, because the events (perhaps delivery from the two hostile kings) will make it appear that you have God present with you. But after He shall be called Jesus, that is, Saviour, because He shall save the whole human race. Wonder not, therefore, O house of David, at the newness of this thing, that a Virgin should bring forth a God, seeing He has so great might that though yet to be born after a long while, He delivers you now when you call upon Him.