The Work of John the Baptist
Luke 3:1-6 describes a bit about the work of John the Baptist, preparing the way for Christ to start His ministry. Luke starts by naming various governors and rulers of various nearby portions of the Roman Empire, and identifying the high priests leading the Jewish people in a religious capacity. He then says that God spoke to John, while John was in the wilderness and that John stepped up to the call of God.
What John was preaching was interesting to some, and offensive to others. This is not unlike what we experience today. The preaching of Jesus is of interest to some, and causes offense to others. In John's case, what he was led to preach and condemn would end up killing him. So it is today for many Christians in the world. In the tribulation period, the consequences of preaching Christ will be even higher for a greater percentage of those who choose Christ after the rapture.
His message got people's attention, and they came from all around to hear him preach,. calling for baptism and repentance to cleanse the soul of sin. This was a radical concept in their day. Remember that as Jewish people, they relied on sacrifices to cleanse them of sin. The thought that cleansing the soul from sin didn't require an animal to die was revolutionary in their lives.
He did this to prepare the way, of course, for Jesus Christ. Jesus was to be the final sacrifice to provide the bridge between man and the Holy God that they served. No more yearly sacrifices. No more requiring an intermediary priest to do the sacrifice and intercede with God. The words he taught are mostly lost to history, just as most of these will be. But God remembers.
He quoted the words of Isaiah, telling of a time that one would be crying in the wilderness, making the way straight for the Lord [Isaiah 40:3-5]. All flesh would see the salvation of God.
The Opposition to John
As with Christ, John's work attracted an element that sought to discredit or destroy it. As noted in Matthew, the Pharisees, Sadducees, and other religious leaders came to watch. In Luke 3:7-20, we see his comments to them, which mirror the account in Matthew. It appears from this passage that they were compared to poisonous vipers, who were coming to be baptized both to be a safeguard in case John was right, and to tear down his work to lift up their own traditions.
He called on them to truly repent of the evil in their hearts. He would say the same to the world today. Repent of the evil that you are either thinking about or actively doing. Turn from your wicked ways and accept Christ as Savior and Lord.
He would say to us, as them, don't depend on your parents or ancestors relationship with God to save you. It is a choice that you must make on your own. God created Adam out of dust. He can raise up other children of your ancestors any time He wants. You aren't special because of who your ancestors were.
Bring forth Christian fruit. If you don't know what that is, read Christ's Sermon on the Mount as a reference. If you aren't bring forth good fruit, beware, because the ax may be at your roots getting ready to cut you down, cut you in pieces, and cast you into the fire to burn forever. He gave some examples they could follow. If you had more than you needed, give to the poor. If you have more food than you need, share. Don't take more than you are owed. Don't oppress the innocent. Don't falsely accuse people. Be content with the wages you are paid.
The people wondered if he was the Christ that was prophesied to come, but he shut down that way of thinking immediately, saying that Jesus who would come was so much above him that John wasn't worthy to even tie his shoelaces. He also promised that Jesus would baptize with the Holy Ghost and with fire [Acts 2]. He would execute judgment in the land when His time came.
He exhorted the people to live righteously, and unfortunately also went against Herod who had taken an improper relationship with Herodias, his brother Philip's wife. He also spoke of all the evil things that Herod had done (such as having all the kids two years old and under killed around Bethlehem). That would eventually land him in prison and cost him his life. But although he had doubts while in prison, I don't think he would have changed a thing. We'll have to wait and hopefully ask him ourselves in heaven.
The Baptism of Jesus Christ
As he was baptizing people, Jesus came to be baptized [Luke 3:21-22]. Although it doesn't get much space here, note that John and the rest of the people around John got to see the heaven above opened up and the Holy Ghost descending like a dove onto Jesus, and heard a voice come from heaven declaring Jesus to be God's beloved son that God was very pleased with.
An event similar to that changed Saul's course of action toward the Christians on the road to Damascus. What would an event like that do for you? Clearly, we aren't going to see any person be called out as the son of God from heaven. That was a one and done sort of thing. But we can read testimonies of many people, like Saul/Paul who have had their lives upended by an experience with God. If you've had a similar experience, share it. Win more people to God.
The Genealogy of Christ
The chapter concludes with Luke 3:23-38 tracing the ancestry of Jesus through Mary's husband Joseph back to Adam. It is in reverse order to what is supplied in Matthew, and there are some spelling differences between the New and Old Testaments, but the lineage is complete, and wasn't debated in the New Testament times, even though some of the people lived in the time between the last written books of the Old Testament and the birth of Joseph and thus didn't have recorded ancestry in the Old Testament.