From A Commentary on Isaiah

“These things in Isaiah were said before the time when the savior had come and before the time when he assumed from a virginal womb our nature and substance, that humanity which he came to save – so that we, who have borne the image of what is earthly, may in turn bear the image of the heavenly (1 Cor 15).  ‘If you would come down,’ as Isaiah writes, ‘and the heaven were opened,’ at your coming in majesty the mountains would overflow and the mountains would quake and be consumed like wax when touched by fire (Isa 64:1).

The heavens opened for Ezekiel, and he saw a great vision (Ezekiel 2). Moses, too, prays in the ‘blessings’ in Deuteronomy: ‘The Lord will open to you his good treasury the heavens, in order to give you a blessing’ (Deut. 28:12). And in the Gospel, John the Baptist is said to have seen the heavens opened and the Holy Spirit descending upon the Lord in the form of a dove (Matt. 3:16). Moreover, it is written, ‘The Lord is a consuming fire’ (Deut. 4:24). Hence, when the text says that at the coming of the Lord the mountains will be consumed and melted like wax, this signifies the powers which stood against him and all who raise themselves up against the knowledge of God…

“And the nations will tremble at your presence” (Isa 64:2) means that they will be stirred, so that what formerly did not move may come to salvation. When he does glorious deeds (64:3), as in the gospel, and works signs which he once displayed in Egypt and in the wilderness, they would confess that they are unable to bear the glory of his coming…The passage is beautiful in the Hebrew, for it makes clear that the words they prayed, ‘O that you would rend the heavens and come down, and the mountains would flow at your presence’ (64:1), had been clearly heard. For they go on to say, ‘You did come down’ (64:3). That is, ‘The Word was made flesh and dwelt among us’ (John 1:14). Indeed, he is ‘Emmanuel, which means, God with us’ (Matt. 1:23).”

St. Jerome (ca. 347-420) is best known for the Vulgate, his translation of the Scriptures into Latin, completed in 405. It was the official translation of the Western Church for over a thousand years. He was one of few church fathers who read Hebrew, and his extensive commentaries include numerous insights from his reading in the language. His feast day is September 30.