The first verse of Acts contained the formal introduction to the book, but the following verses fill it out a bit more. These verses refer to the Lord’s resurrection appearances, and the proofs He gave His disciples that He was in fact alive. Second, He taught them about the kingdom, and told them to wait in Jerusalem until they had been given kingdom power. When that power had descended upon them, they would be ambassadors of that kingdom out to the ends of the earth. And then last, the angels promised that Christ would at some point return in the same way that He left, meaning that He would descend from the sky.