Palm Sunday worship is a long-standing tradition in the Church when we celebrate Jesus' entrance into Jerusalem in preparation for the Passover Meal. He was welcomed with fanfare in royal fashion. However, later that week, he would be condemned to die by the same crowd.
We, as Christians, see Jesus as God's long-promised Messiah, our Savior and King.
Check out the following video from Chuck Knows Church for a lighthearted explanation: