Question: "What does it mean to repent and believe the gospel (Mark 1:15)?"
Answer: After the arrest of John the Baptist, “Jesus came into Galilee, proclaiming the gospel of God, and saying, ‘The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel’” (Mark 1:14–15, ESV). Jesus’ exhortation for His listeners to repent indicated that they needed to change their minds. That He told them to believe in the gospel indicated how they needed to change their minds. Mark refers to Jesus’ message as “the gospel of God” (verse 14, ESV), or “the good news of God.” It was good news that the kingdom was at hand, and Jesus was preparing His listeners for how to be part of that kingdom.
Many in Jesus’ audience thought they were already righteous and would gain entrance to the kingdom of God because of their connection to Abraham and Moses and because they were keeping the laws God had given to Israel through Moses. Matthew 5—7 records Jesus’ Sermon on the Mount, in which Jesus taught that His listeners should change their minds about how they could be part of His kingdom. Their connection to Abraham and Moses wasn’t enough, and their supposedly righteous deeds were not enough. Those things are not what God requires as the standard of righteousness. Instead, Jesus explained that they needed to have a true, internal righteousness, and they did not yet have that. It wasn’t just a king that they needed—they needed a savior. Sadly, only a few would recognize that need.
Jesus proclaimed that the people needed to repent and believe in the gospel because the kingdom of God was at hand. God’s eternal kingdom is currently based in heaven. But, in passages like 2 Samuel 7 and Revelation 19—20, God promises that His kingdom will at some point in the future come to earth in a physical form. The kingdom was at hand, or near, because Jesus the King had come to earth, presenting the kingdom and the good news about that kingdom and how one can be part of it—by believing in the gospel. Unfortunately, Jesus’ audience wasn’t yet prepared for the kingdom, because they hadn’t yet recognized that they needed the Messiah to make them righteous, and that Jesus was the Messiah.
Jesus’ message was truly good news, and the people needed to change their minds from unbelief to belief. They needed to believe in the Lord—as Abraham had done many years prior (Genesis 15:6)—to gain the righteousness that would allow them to be part of God’s kingdom. They needed to repent (change their minds about how they could enter the kingdom) and believe in the gospel now, because the kingdom of God was close at hand. Of course, some did change their minds about how they could be righteous, and they believed in Jesus, but most of the leaders and the nation as a whole did not believe (Mark 3:22–30). Because of that rejection, Jesus delayed the kingdom and shifted His focus and ministry to providing the sacrifice to pay for the sins of the people.
One day Jesus will return to the earth as King (Revelation 19—20), and, because of what the Bible tells us about the future, we know that we also need to “repent and believe in the gospel for the kingdom of God is at hand.” We need to change our minds from unbelief to belief and recognize that we are saved by grace through faith and not by our own works (Ephesians 2:8–9). When we believe in Christ, we are already transferred to His kingdom (Colossians 1:13), and, because His kingdom isn’t on earth yet, we ought to set our mind on the things above where He is, rather than on the things of earth (Colossians 3:1–4).