Updated: Oct 12, 2021
v1-12 - We are reading the New Testament, but John the Baptist is really the last of the Old Testament prophets.
Like many other Old Testament prophets, John was an odd duck.
His clothing and diet seem weird to us now, but they even seemed weird two thousand years ago when he showed up.
This oddness may have been one of the things that drew so many people out to the middle of nowhere to hear him preach and to be baptized (baptism was around in the Old Testament as well as a rite of purification after repentance).
John's message is consistent with the prophets as well: REPENT.
The Pharisees and Sadducees who came to check out what John was doing (likely because they were jealous of the crowds John was attracting) were professional repenters.
Nobody repented in a finer fashion than did they. Of course, it was all a big show and they weren't truly repenting of anything, which is why John lights into them so aggressively.
John makes it clear that once we've confessed and repented of sin, those who are truly God's children will live in a way that reflects their repentance.
v13-17 - When John's cousin Jesus showed up along with the crowds to be baptized, John initially refused.
From John's perspective, it didn't make any sense for Jesus to go through this repentance and purification ritual because Jesus had nothing to repent of or be purified from.
Jesus' answer changes John's mind:
it is proper for us to do this to fulfill all righteousness (v15).
Jesus' mission was to come and live the perfect life of obedience to God that man was supposed to have lived.
But before He could fulfill that mission, He had to be identified with sinful man in a sinless way.