Ambrose of Milan — as excerpted in the Catena Aurea on Luke 3:21-22

“But the cause of our Lord’s baptism He Himself declares when He says, Thus it becomes us to fulfil all righteousness. But what is righteousness, except that what you would have another do to you, you should first begin yourself, and so by your example encourage others? Let none then avoid the laver of grace, since Christ avoided not the laver of repentance.”