For it is not true that Christ then descended on Jesus: nor are Christ and Jesus two distinct persons, but the Word of God, the Savior of all and the Ruler of heaven and earth, is Jesus. He took flesh; he was anointed by the Father with the Spirit and became Jesus Christ as also Isaiah says ‘there shall spring forth a rod from the root of Jesse, and a flower shall come up from this root, and the Spirit of God shall rest upon him, the spirit of wisdom and understanding’ . . . (Isaiah 11:1-2)
And again Isaiah, foretelling his anointing, and the end for which he was anointed, says, ‘The Spirit of God is upon me, wherefore he has anointed me, and sent me to preach good tidings to the lowly’ . . . (Isaiah 61:1) Therefore the Spirit of God descended on him; the Spirit of him who through the prophets had promised that he would anoint him, in order that we might receive of the abundance of his unction and be saved.
God promised through the prophets to ‘pour out this Spirit upon his servants and handmaidens in the last days, that they may prophesy.’
And the Spirit descended from God on the Son of God, made son of man, and with him became accustomed to dwell among the human race and to ‘rest on’ men and to dwell in God's creatures, working the Father's will in them, and renewing them from their old state into the newness of Christ.
St Irenaeus of Lyons