What does Acts 1:6 mean?

Jesus has spent forty days since being raised from the dead giving the disciples information on the kingdom of God (Acts 1:3). Now, He is about to ascend into heaven so the Holy Spirit can come (John 16:7). The disciples are still confused. For three years, Jesus has spoken of the coming of the kingdom—surely it will happen now.

During those three years, Jesus told many parables about the kingdom of God, also known as the kingdom of heaven. Matthew, alone, mentions "the kingdom of heaven" thirty-one times. "Kingdom" is from the Greek basileia. It can mean a literal territory ruled by a king, but Jews also use it to mean the power and authority of the Messiah over Israel and the restoration of an independent Israel. Jesus has promised the disciples that in His kingdom they will sit on twelve thrones and judge the tribes of Israel (Matthew 19:28; Luke 22:30). Throughout Jesus' ministry, they have been anxious to see this happen, but Jesus has specifically told them that only God knows when (Mark 13:32).

One of the truths the disciples can't comprehend quite yet (John 16:12) is that the kingdom of God is more than just Israel gaining independence from Rome and being a sovereign nation again. The kingdom of God includes the restoration of the hearts of His followers (Ezekiel 36:26) from every tribe and nation (Revelation 7:9). The disciples are worried about when Jesus' kingdom will come; Jesus wants them to concern themselves with who will be in that kingdom. They need to find the sheep of other folds (John 10:16). The kingdom can't fully come until they have been Jesus' witnesses around the world (Acts 1:8) to the point that the Gentiles have been sufficiently reached (Luke 21:24; Romans 11:25). Until then, Israel will become less of a nation, not more. In fact, just a few decades after the events depicted by Luke, Jerusalem will be destroyed and the Jews will be scattered all over the world.