Luke 3:21-22
21 *Now it came to pass, when all the people were baptized, that Jesus also being baptized, and praying, heaven was opened:
22 And the Holy Ghost descended in a bodily shape, as a dove upon him: and a voice came from heaven: *Thou art my beloved Son, in thee I am well pleased.
Ver. 21. The motive of his baptism, as he himself informs us, was, that he himself might fulfil all justice. What is here meant by justice, but that obligation of doing first ourselves what we wish others to do? --- Let no one then refuse the laver of grace, since Christ did not refuse the laver of penance. (St. Ambrose) --- Although all our sins are forgiven in baptism, still the frailty of the flesh is not yet perfectly strengthened. For, after passing this red sea, we rejoice at the destruction of the Egyptians, but still we must fight with assurance of the grace of Christ, against the enemies we shall undoubtedly meet with in the desert of this world, till at length we arrive at our true country. (Ven. Bede) --- It is said the heavens were opened, because they had been hitherto shut. The sheepfolds of heaven and earth are now united under the one Shepherd of the sheep: heaven is opened, and man, though formed of the earth, is admitted to the company of angels. (St. Chrysostom)
Ver. 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.)