Luke 3:22

The reason why the Holy Ghost shewed himself in the shape of a dove, was because he could not be seen in the substance of his divinity. But why a dove? To express that simplicity acquired in the sacrament of baptism. Be ye simple as doves; to signify that peace bestowed by baptism, and prefigured by the olive branch which the dove carried back to the ark, a true figure of the Church, and which was the only security from the destructive deluge. (St. Ambrose) — You will object: Christ, though he was God, would not be baptized till the age of 30, and do you order baptism to be received sooner? When you say, though he was God, you solve the difficulty. For, he stood not in need of being purified at all; of course, there could be no danger in deferring his baptism. But you will have much to answer for, if, being born in corruption, you pass out of this world without the garment of incorruption. (St. Gregory of Nazianzus, orat. 40.)

6. We have therefore no reason to depend upon our external privileges and professions of religion, because God has no need of us or of our services, but can effectually secure by his own honour and interest without us. If we were cut off and ruined, he could raise up to himself a church out of the most unlikely,—children to Abraham even out of stones.

Verses 21-22 Christ did not confess sin, as others did, for he had none to confess; but he prayed, as others did, and kept up communion with his Father. Observe, all the three voices from heaven, by which the Father bare witness to the Son, were pronounced while he was praying, or soon after, Lu. 9:35 ; Joh. 12:28 . The Holy Ghost descended in a bodily shape like a dove upon him, and there came a voice from heaven, from God the Father, from the excellent glory. Thus was a proof of the Holy Trinity, of the Three Persons in the Godhead, given at the baptism of Christ.