This means that Peter is about to explain the meaning of what the people had witnessed. This can be stated in active form. AT: "know this" or "let me explain this to you" (See: [[rc://en/ta/man/translate/figs-activepassive]])
"It is only nine o'clock in the morning." Peter expected his audience to know that people do not get drunk that early in the day. (See: [[rc://en/ta/man/translate/figs-explicit]])