Why did John the Baptist preach "Repent, for the kingdom of heaven is at hand"?
John the Baptist preached repentance because the King was present. Christ was on the scene, about to present Himself to Israel as the promised Messiah and King. The people therefore needed to prepare spiritually through repentance and the baptism of repentance that John proclaimed.
Les explains that in Matthew chapter 3, John the Baptist comes on the scene preaching in the wilderness of Judea, saying, “Repent ye... for the kingdom of heaven is at hand.” Les asks why John said that, and answers that it was because the King was there. Christ was on the scene, and He was about to present Himself to the nation of Israel as their promised Messiah and King. Therefore, the people were to prepare for that spiritually with repentance and the baptism of repentance that John preached. Les also notes that the term “the kingdom of heaven” is rampant throughout Matthew, and he points to Matthew 4:17 as another example.
And saying, Repent ye: for the kingdom of heaven is at hand.