11 Then he remembered the days of old, Moses, and his people, saying, Where is he that brought them up out of the sea with the shepherd of his flock? where is he that put his holy Spirit within him?
(Vers. 11 seqq.) And he remembered the days of old, Moses and his people. Where is he who brought them up from the sea with the shepherds of his flock? Where is he who put his holy Spirit in the midst of them? He who caused his glorious arm to go at the right hand of Moses, who divided the waters before them to make for himself an everlasting name. He led them through the depths like a horse in the desert, they did not stumble. Like a beast going down into the valley, the Spirit of the Lord was their guide. So you led your people, to make for yourself a glorious name. LXX: And he remembered the days of old, Moses and his people, saying: Where is he that brought them up out of the sea with the shepherd of his flock? where is he that put in the midst of them the spirit of his Holy One? He led them by the right hand of Moses with his glorious arm, dividing the waters before them, to make himself an everlasting name. He led them through the deep, as a horse in the wilderness, they stumbled not. As a beast goeth down into the valley, the spirit of the Lord caused him to rest: so didst thou lead thy people, to make thyself a glorious name. The Lord, who became the protector of the adversaries of the people of Judah, who provoked his Holy Spirit to anger, and he defeated them: he remembered the ancient days, when Moses interceded for them in the wilderness, saying: Either forgive them this sin, or if you do not, blot me out from the book which you have written (Exodus 32:31-32). So Isaiah, recalling the story of old, says: Where is the Moses who led them out of the Red Sea? Where is the shepherd of the sheep? Where is he who labored with the other shepherds of the flock of the Lord? Who obtained and bestowed the Spirit of God through his prayers and supplications on the flock of the Lord? Or surely should it be understood this way: Where is that mercy of the Lord, by which he once had pity on his people, so that he would also grant them the grace of the Holy Spirit? He who led Moses, his servant, with the arm of his majesty to the right side, not to the left; he who split the waters before them, to make for himself an everlasting name, so that his power would be spoken of even to this day? For He led His people through the immense depths of water, like a horse through a wilderness, and beasts through a plain, and the Spirit of the Lord was their guide, that is, the flock of the Lord. (Exodus 14). Now by this Spirit we must understand the Angel, who was the guide of the people of Israel, according to what is written: He makes His angels spirits, and His ministers a flaming fire (Psalm 104:4). And in the Letter to the Hebrews: Are they not all ministering spirits, sent forth to minister for those who will inherit salvation? (Hebrews 1:14). Let us consider that which is written in the Acts of the Apostles: The Spirit of the Lord caught away Philip, and the eunuch saw him no more (Acts 8:39). Should we understand this as referring to an angel? There are those who testify that it was an angel working through the Holy Spirit. We are exploring the obvious in order to dwell on the obscure.
[AD 420] Jerome on Isaiah 63:11-14