Luke 3:21

The evangelist mentioned John's imprisonment before Christ's being baptized, though it was nearly a year after it, because he would finish the story of John's ministry, and then introduce that of Christ. Now here we have, I. A short account of Christ's baptism, which had been more fully related by St. Matthew. Jesus came, to be baptized of John, and he was so, Luk 3:21, Luk 3:22. 1. It is here said that, when all the people were baptized, then Jesus was baptized: all that were then present. Christ would be baptized last, among the common people, and in the rear of them; thus he humbled himself, and made himself of no reputation, as one of the least, nay, as less than the least. He saw what multitudes were hereby prepared to receive him, and then he appeared. 2. Notice is here taken of Christ's praying when he was baptized, which was not in Matthew: being baptized, and praying. He did not confess sin, as others did, for he had none to confess; but he prayed, as others did, for he would thus keep up communion with his Father. Note, The inward and spiritual grace of which sacraments are the outward and visible signs must be fetched in by prayer; and therefore prayer must always accompany them.

— Matthew Henry's Concise Commentary (public domain)

BAPTISM OF AND DESCENT OF THE SPIRIT UPON JESUS. (Luk 3:21-22) when all the people were baptized--that He might not seem to be merely one of the crowd. Thus, as He rode into Jerusalem upon an ass, "whereon yet never man sat" (Luk 19:30), and lay in a sepulchre "wherein was never man yet laid" (Joh 19:41), so in His baptism He would be "separate from sinners."

— Jamieson-Fausset-Brown Commentary (public domain)