What does Acts 1:9 mean?

This moment was also recorded in Luke 24:51. It is forty days after Jesus' resurrection, and He has spent that time telling His disciples about the coming kingdom of God (Acts 1:3). Any hope that this kingdom includes an Israel freed from Roman rule and twelve thrones for the twelve apostles (Luke 22:30) now rises into the sky with Jesus.

God is often represented by clouds in the Bible. In Exodus, a pillar of cloud led the Israelites through the wilderness (Exodus 13:21). When the Israelites camped at Mt. Sinai, God covered the mountain in cloud and smoke to show the people the authority He was giving Moses (Exodus 19:9, 16–18). When Solomon brought the ark of the covenant into the new temple, God filled the whole building with a cloud of His glory so thick the priests had to flee (1 Kings 8:10–11). When God showed Peter, James, and John the glory of Jesus during the transfiguration, He spoke to them from a cloud (Mark 9:7). And when Jesus will return, for both the rapture (1 Thessalonians 4:16–17) and the second coming (Revelation 1:7), He will come with clouds.

All such cases illustrate the shekinah glory of God—the glory of God that dwells with His people. God's glory is so great we can only experience it if it is veiled as if by clouds. Soon, we will see God clearly (2 Corinthians 3:12–18).