to them

"to his disciples"

leads you astray

Jesus is warning his disciples not to be deceived by anyone about what will happen. Here "lead astray" is an idiom for "deceive." AT: "deceives you concerning what will happen" (See: rc://en/ta/man/translate/figs-explicit and rc://en/ta/man/translate/figs-idiom)

Possible meanings are 1) "claiming my authority" or 2) "claiming that God sent them." (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-idiom)

"I am the Christ"

Here "lead astray" is an idiom for "deceive." AT: "will deceive many people" (See: rc://en/ta/man/translate/figs-idiom)