Jesus is referring ahead to his death. The word for "suffer" here refers to an unusually difficult or painful experience.
# For I say to you
Jesus uses this phrase to emphasize the importance of what he will say next.
# until it is fulfilled
This can be stated in active form. Possible meanings are 1) until the purpose of the Passover Festival is accomplished. AT: "until God fulfills it" or "until God completes the purpose of the Passover Festival" or 2) "until we celebrate the final Passover Festival" (See: [[rc://en/ta/man/translate/figs-activepassive]])