For several reasons, it is significant that John the Baptist was preaching, “Repent, for the kingdom of heaven is at hand” (Matthew 3:2, ESV).
Malachi 3:1 is a prophecy that a messenger would come who would prepare the way for Israel’s Messiah. When the Messiah came, that would signal the arrival of the King, with the Day of the Lord to follow and, when that was complete, the beginning of the Messianic Kingdom. John was that messenger, and his mission was to prepare the people to receive their Messiah. John’s call for the people to repent indicated that they needed to change their minds. From Jesus’ own preaching of that same message (e.g., Matthew 4:17), we find that the people thought they were righteous and would have access to the kingdom of God because of their relationship to Abraham and Moses and because of their outward obedience to the laws God had given Israel through Moses. In the Sermon on the Mount (Matthew 5—7), Jesus makes it clear that the people needed to change their minds about how a person becomes part of His kingdom. Their self-perceived righteousness was not enough—their heritage and works were not what God required. Instead, God required that the people have a true, internal righteousness that they didn’t yet possess. Not only did they need a king, but they needed a savior; unfortunately, many of them did not realize that need.
In order to make the need clear, John and Jesus proclaimed that the people needed to “repent, for the kingdom of heaven is at hand,” or “has come near” (CSB). God has an eternal kingdom that currently resides in heaven. But passages like 2 Samuel 7 and Revelation 19—20 prophesy that God’s kingdom will one day come to earth in a physical form. Because this will be a heavenly kingdom changing location to earth, John and Jesus (as recorded in Matthew) usually refer to it as “the kingdom of heaven” (or, literally, “the kingdom of the heavens”).
The kingdom was “at hand” or “near” in Jesus’ day because the King had come. But the people weren’t ready yet for the kingdom because they hadn’t yet understood their need for the righteousness that the King would provide. Because of that lack of understanding and the arrival of the King, John’s and Jesus’ message was vitally important—the people truly needed to repent (change their minds about how they could enter the kingdom). While many individuals did change their minds about how they could be righteous, the leaders and the nation as a whole did not (Matthew 12—13), and they rejected Jesus as their King. As a result, Jesus delayed the kingdom and died to pay for the forgiveness of sins so that those who believe in Jesus can be part of His kingdom forever.
In Revelation 19—20 Jesus returns to earth as the King, and He sits on a throne ruling over Israel for one thousand years. After that thousand years, He fulfills His role as Judge, and after judgment is fulfilled, His kingdom continues in a new earth for eternity. Because of what the Bible tells us about the future, we know that we also need to “repent, for the kingdom of heaven is at hand.” We need to change our minds about how we become righteous and rely on God’s grace and Jesus’ saving work on the cross, not on our own works and efforts. For those who have believed in Him, we have already been transferred to His kingdom (Colossians 1:13), but because His kingdom isn’t here yet—because the King isn’t here yet—we need to set our mind on the things above where He is, rather than on the temporary things of earth (Colossians 3:1–4).