John the Baptizer is a colorful prophetic figure who introduces the story of Jesus in all four Gospels.
He dresses like Elijah, and he sounds like Isaiah or Amos. In the Matthean account, as in Mark whom the First Evangelist is closely following, we are given no inkling that the two men might be related. It is interesting as well that in both the Matthean and Markan accounts John is introduced to us as the fulfillment of Isaiah 40:3.
What is compelling about that text is it can be punctuated in two ways: "The voice of one crying in the wilderness: 'Prepare the way of the Lord.'" Or should it read "The voice of one crying: 'In the wilderness, prepare the way of the Lord'?" The text of Isaiah suggests the latter reading so that it is in the wilderness where "the highway of our God" is to be paved. It would appear that this is how John the Baptizer, like the Qumran community which also had this text as a theme verse, understood it. John is in the chalk wilderness of Judea, near the Jordan and the Dead Sea, calling Jews to repentance lest the judgment, which begins with the household of God, fall on them forthwith. It is entirely possible John had been part of the community at the Dead Sea and then went out on his own to call Israel in general to repentance, connecting the call with a baptism in the Jordan.
Repentance, or metanoia, to use the Greek word, refers to far more than a simply being or saying one is sorry for past sins, far more than mere regret or remorse for such sins. It refers to a turning away from the past way of life and the inauguration of a new one, in this case initialized by an act of baptism.
One of the mistakes sometimes made in interpreting this text is assuming that the sort of baptism John called his fellow Jews to is to be equated with the baptism later practiced by Christians on all and sundry. The problem with this assumption is that John is calling for repentance of those who already believed in the Biblical God and in his Word--- namely Jews, including the Jewish leadership, whereas Christian baptism is treated by Paul in Romans 6 as an initiation rite for those converting to Christ, a rather different matter (see Witherington Troubled Waters, Baylor 2005).
What is interesting about John's call to repentance and baptism is that he seems to be offering a way for remission of sins without requiring going to Jerusalem and offering a sacrifice. If this is correct, it explains why the Jerusalem leadership would have been uneasy with John the prophet, and it may explain the adversarial attitude John had towards them in Matthew 3:7-10 where he calls them snake spawn!
Equally interesting is John's affirmation that merely being a descendant of Abraham or even a pious person of faith in itself does not exempt that person from the coming judgment, if they do not change their ways. John foresees a judgment falling on Israel separating the wheat from the chaff, something Jesus also seems to have envisioned as well.
Preaching a text like this one at Christmas time may be challenging, but in fact the Advent season, when many will be in church who would not normally darken its door, it is an appropriate time to call people back to the Lord and to the amendment of their lives.
There is also the possibility of dealing with the theme of our being like John, and of asking the question, in what way are we preparing the way of the Lord, and making straight a path for our God in our own and other's lives?
A further theme in this passage is the presentation of John's humility, knowing there would be the One who comes after him whom he knows he is not even worthy of being the household servant of (the task of unlacing the sandals was left to the household slave). Notice, as well, the contrast between John's baptism and that of Jesus' in verse 11. So far as we know, Jesus never baptized anyone (see the clarification in John 4:1-2), though even his earliest disciples, perhaps especially those who had previously followed John, did. Jesus, according to John, would baptize people with the far more potent and life changing Holy Spirit.