Here "leads you astray" is a metaphor for persuading someone to believe something that is not true. Alternate translation: "Be careful that no one deceives you ... and will deceive many people" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "name" refers to "in the authority" or "as the representative" of someone. Alternate translation: "many will claim that they have come as my representative" or "many will say they speak for me" (See: [[rc://en/ta/man/translate/figs-metonymy]])