This can be stated in an active form for clarity. AT: "Then John's disciples and a Jew began to argue" (See: [[rc://en/ta/man/translate/figs-activepassive]])
In this phrase, "look" is a command meaning "pay attention!" AT: "Look! He is baptizing" or "Look at that! He is baptizing" (See: [[rc://en/ta/man/translate/figs-explicit]])