What was the main message of John the Baptist?

According to Matthew 3:1-2, John the Baptist appeared in the wilderness of Judea, preaching: "Repent, for the kingdom of heaven is at hand" (also rendered "the kingdom of God is at hand" in Mark 1:15). This was the central and defining message of John's ministry.

John's role was that of a forerunner - one who prepared the way for the coming Messiah. His message of repentance called people to turn away from sin, confess their wrongdoing, and undergo baptism as an outward sign of inner transformation. He preached this in fulfilment of the prophecy of Isaiah 40:3: "A voice of one calling in the wilderness, 'Prepare the way for the Lord, make straight paths for him.'"

While "Believe in Jesus" became central to later Christian preaching, it was not John's primary message; John pointed people toward one who would come after him. "Obey the Ten Commandments" summarises Mosaic law but was not John's distinctive proclamation. "Love your enemies" is a teaching from Jesus' Sermon on the Mount (Matthew 5:44), not a message associated with John the Baptist. The urgency of John's preaching centred specifically on repentance in light of the approaching kingdom.