John Gill Commentary Matthew 24:25

"Behold, I have told you beforehand." — Matthew 24:25 (ASV)

Behold, I have told you before . ] Meaning not before in this discourse, though he had in (Matthew 24:5Matthew 24:11) also signified that false Christs and false prophets should arise, but before these things came to pass.

So that they had sufficient notice and warning of them, and would be inexcusable if they were not upon their guard against them.

And which, when they came to pass, would furnish out a considerable argument in proof of him as the true Messiah, against all these false ones, showing him to be omniscient. And so it would serve to establish their faith in him, and be a means of securing them from such deceivers.