John Chrysostom
Because after His baptism Christ was to put an end to the Law, He therefore came to be baptized at this age, that having so kept the Law, it might not be said that He cancelled it, because He could not observe it.
Then, that is when John preached, that He might confirm his preaching, and Himself receive his witness. But as when the morning-star has risen, the sun does not wait for that star to set, but rising as it goes forward, gradually obscures its brightness; so Christ waited not for John to finish his course, but appeared while he yet taught.
In this he shews that Christ after this baptized John; which is expressly told in some apocryphal booksi. Suffer now that I fulfil the righteousness of baptism in deed, and not only in word; first submitting to it, and then preaching it; for so it becometh us to fulfil all righteousness. Not that by being baptized He fulfils all righteousness, but so, in the same manner, that is, as He first fulfilled the righteousness of baptism by His deeds, and after preached it, so He might all other righteousness, according to that of the Acts, All things that Jesus began both to do and to teach. (Acts 1:1.) Or thus, all righteousness, according to the ordinance of human nature; as He had before fulfilled the righteousness of birth, growth, and the like.
He comes to baptism, that He who has taken upon Him human nature, may be found to have fulfilled the whole mystery of that nature; not that He is Himself a sinner, but He has taken on Him a nature that is sinful. And therefore though He needed not baptism Himself, yet the carnal nature in others needed it.
That Thou shouldest baptize me there is good cause, that I may be made righteous and worthy of heaven; but that I should baptize Thee, what cause is there? Every good gift comes down from heaven upon earth, not ascends from earth to heaven.