Luke 3

It is clear that it is the "the word of God" that called John into ministry; and it was during a time when there were corrupt and cruel political and religious leaders.  John fulfilled the prophecy in Isaiah as he preached a "baptism of repentance for the forgiveness of sins".   In the context of Luke 3, this meant that it was a water baptism similar to when Gentiles converted to Judaism to display ceremonial cleansing and adoption in to the covenant, and that they needed to turn from their wicked ways and live their lives producing "fruit in keeping with repentance".     This would prepare their hearts and lives to be ready for the salvation through Christ for the forgiveness of their sins.  John didn't "sugar coat" his message, and clearly talked about the coming judgment ("ax", "fire", "winnowing fork"), even calling his audience a "brood of vipers" fleeing from the coming wrath.   

Jesus was sinless and perfect, and did not need to be baptized.   But, He said to permit it at this time.   He was being an example, identifying with sinful man he was going to save, and allowing for the affirmation of His Messiahship through the presence of the Trinity at His Baptism - the Son being baptized, the Holy Spirit descending from heaven, and the voice of the Father saying "You are my Son, whom I love; with you I am well pleased."

 In the start of His ministry, Luke, through His geneology, once again reminds us that Jesus is of the line of David, and is the "son of Adam, the son of God."   This points out that Jesus is the Messiah, is fully Man, and is fully God; and leads to what Paul will later talk about that Jesus is the second Adam.  This geneology different from Matthew's, is likely that of Mary's (the physical line) while Matthew lists Joseph's (the legal line, in this patriarchal society).

This passage reminds us that God has His perfect time (calling John at this time, when he has already been in the wilderness for years), that He fulfills His prophecies and promises, that He will judge, but that He also provides the way to salvation.   We are to prepare our lives by making our paths straight (filling valleys, leveling mountains and hills, straightening the crooked, smoothing the rough), producing good fruit through compassion and integrity, and waiting for Him in humility.