So there wasn't a big jump from Acts 1:7 to Acts 1:9 which made people go "wtf, did I fall asleep and miss something?". Plot continuity is very important, and this was known even in the time of Jesus.

Acts 1:8 reveals one of the purposes Luke had in writing the history. Luke wanted to show how the church penetrated the world of his day in ever-widening circles (Jerusalem, Judea, Samaria, and the ends of the earth) until it reached Rome.

To motivate Christians to the work that was ahead for them. Some today, disparage Christian Witnesses who carry this Christian commission, calling them “proselytizers ” and criticizing them. This is probably one of the most astounding prophecies in the Bible here at Acts 1:8. Shortly before he ascended to heaven, Jesus told his faithful followers: “You will receive power when the holy spirit arrives upon you, and you will be witnesses of me . . . to the most distant part of the earth.” What an enormous undertaking this would prove to be. To proclaim God’s word throughout the earth must have seemed a daunting assignment to that handful of disciples who received it. Think about what was involved. They would have to help the people to understand the good news of God’s Kingdom. (Matthew 24:14) Bearing witness to Jesus also required sharing his powerful teachings with others and explaining his role in Jehovah’s purpose. Even more, the work included making disciples of people and then baptizing them., which was to be done worldwide. See Matthew 28:19, 20. Jesus assured his followers that holy spirit would be with them in carrying out the work that he had given to them. This work will continue right up until God decides that it has been accomplished.