“publicly confessing.” The Greek verb is exomologeō (#1843 ἐξομολογέω), and it means to confess or admit openly or publicly. In this instance it is a plural participle, and indicates that the confession was connected with the baptism: they confessed their sin as they were being baptized, i.e., just before going under the water. The form of the verb indicates that they openly confessed their sin, not just whispered it to John. John Peter Lange writes: “The compound ἐξομολογούμενοι denotes public confession” (Lange’s Commentary; cp. Meyer, who points out that public confession is also indicated in Acts 19:18 and James 5:16).
The public confessions at the baptism of John showed how serious the people were about being saved and entering the Kingdom of Heaven after they heard from John that the Kingdom was about to arrive (cp. John’s message in Matt. 3:2, “the Kingdom of Heaven is near”). The “Kingdom of Heaven” was the kingdom promised in the Old Testament and ruled by Christ where no one was sick, the government was just, there was an abundance of food, and there was no war or crime.
People wanted to get into that kingdom, and they set aside their reservations and, out in the water with John, openly confessed their sins. Their being immersed in the waters of the Jordan then symbolized the death of the old ways and rebirth or resurrection into a new life, which they would then have to live out in the flesh day after day. In contrast to the common people, the religious leaders such as the Pharisees refused to be baptized by John, no doubt in part because they had no intention of openly confessing their sin (Luke 7:30).
We may gain some insight into part of the reason why God spoke from heaven and said about Jesus, “This is my beloved Son, in whom I am well pleased,” when we contrast what occurred with the common people and what happened with Jesus. The common people all openly confessed their sin in the hearing of the crowd, but of course Jesus did not do that. It is possible that there were people in the crowd that were confused about Jesus and wondered why he did not confess any sin, but the loud voice from heaven would have made it quite clear that God was pleased with Jesus, as well as testify to the crowd who Jesus was. The voice was not for John’s sake. John knew who Jesus was, although miraculous confirmation is always welcome. The voice was for the crowd’s sake. Also, there is little doubt that news of the voice got around, which would have only heightened the Messianic expectation that was already quite high due to things such as the teachings of John.
[For more on John’s baptism, see the commentary on Mark 1:4. For more on the Messianic Kingdom on earth, see commentary on Matthew 5:5, “inherit the earth”].