Final answer:
Christians celebrate Palm Sunday to commemorate the “Triumphal Entry into Jerusalem” as described in the Bible.
Step-by-step explanation:
Christians celebrate Palm Sunday to commemorate the “Triumphal Entry into Jerusalem” as described in the Bible. This event is narrated in the Gospels of Matthew, Mark, Luke, and John. Jesus rides into Jerusalem on a donkey while the crowd hails him, throwing cloaks and palm branches on the road before him.