What does Revelation 3:20 mean?

This verse pictures Jesus standing outside the church at Laodicea and knocking at its door to be welcomed and admitted into the church. He does not force himself upon the church, but patiently waits to be invited in. Luke 24:28–32 relates that Jesus and two of His followers were walking to Emmaus, where the two lived. When they reached Emmaus that evening, Jesus acted as if He were going further, but the two followers of Jesus urged Him to stay with them. Having received their invitation, Jesus entered their home. If the church at Laodicea had invited Jesus to enter, undoubtedly He would have entered the church, but the church did not invite Him in. So Jesus looked for an invitation from any responsive individual. He promised to fellowship with whoever would hear His voice and open the door.

Although this verse is often used as an invitation to an unbeliever to receive Jesus as Savior, it applies directly to any church that is apathetic like the Laodicean church. Jesus is not unwilling to restore them to a better state, but they need to demonstrate their willingness to obey God.