Matthew 1:22

Now all this was done
These are not the words of the Angel, but of the Evangelist; observing that Mary's being with child of the Holy Ghost, and her conception in such an extraordinary manner, whilst a pure virgin, before she and Joseph came together, who though espoused to him, was untouched by him, were all brought about in this way, and with such circumstances,

that it might be fulfilled which was spoken of the Lord by the
Prophet;
that is, the Prophet Isaiah, and so some copies read. The passage referred to is in ( 7:14 ) what is there spoken was by divine inspiration; it was spoken of the Lord by the Prophet; the Spirit of the Lord spake by him. Prophets and holy men formerly, spake as they were moved by the Holy Ghost; so that what they said is to be looked upon as the word of God. Now between the prophecy of Isaiah referred to, and the fact here recorded by the Evangelist, is an entire agreement: the prophecy shows the will, counsel, and determination of God about this matter; the accomplishment of it, the faithfulness and veracity of God in his word; the prediction declares that the thing would be, and the thing itself was done, that what was spoken might be fulfilled; not merely by way of accommodation, or in a typical and mystical, but in a strict, proper and literal sense.