This can be stated in active form. Alternate translation: "This is what the prophet Malachi wrote long ago about John the Baptist" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here "your" is singular, because God was speaking to the Messiah in the quotation. Also, "face" refers to the whole person. Alternate translation: "in front of you" or "to go ahead of you" (See: [[rc://en/ta/man/translate/figs-you]] and [[rc://en/ta/man/translate/figs-synecdoche]])
This is a metaphor that means the messenger will prepare the people to receive the Messiah's message. (See: [[rc://en/ta/man/translate/figs-metaphor]])