Warning About False christs
In this passage, Jesus gives another warning about false christs and prophets. This repetition underscores His concern for us to be alert to the deceptions of those who would come in the disguise of those annointed by the One True God. We must certainly be on the alert for the many cults and religions who claim to teach the truth, but whose end is a ie and death. But in this context, I believe Jesus is also preparing us for the ultimate deception spoken of in Revelation 13 when the 'beast' emerges to deceive the world and cause them to worship him. A second beast will perform great 'signs' in order to deceive the world, and mark those who worship the first beast with a seal that will result in their inevitable destruction.
Jesus warns His disciples to be prepared lest they become entrapped in the deception as well. He emphasizes that His coming will be as 'lightning' in the sky, and not from the ground, even as the angels foretold at His ascension.