What does Matthew 24:28 mean?

Jesus has been clarifying to His disciples that His return, the second coming, will not be a secret. They should not believe lies from false prophets and false teachers that He has come back and is hiding out somewhere. He doesn't want them to be led astray by anyone claiming to be Him or the "real" Messiah (Matthew 24:23–26). Instead, Jesus has said that His return will be as public and unmistakable as a blast of lightning across the sky. Everyone will see, everyone will know. They will not be left to wonder or investigate (Revelation 19:11–15).

The proverb Jesus quotes here might seem bizarre, given the context. However, the point is entirely in line with His overall message. You can't hide a fallen body in the open, especially in a wilderness environment, where the presence of vultures circling would quickly it give it away. In the same way, there will be obvious evidence that Jesus has returned to make it clear to everyone that He is back.

The short version of Jesus' message about His return is this: if there is any doubt, then He has not yet returned.