Jesus enters Jerusalem, where the crowds hail him as the blessed one who comes in the Lord's name. This kingly acclaim doesn't last. Jesus is soon betrayed, condemned and crucified.
This Mass is the only one in the Church year that begins with a Gospel reading. It is part of the entrance and follows the blessing of the palms.
The blessed palms we display in our homes are "sacramentals"–sacred signs that help us to cooperate with grace. Later, churches collect and burn the palms to provide the ashes that will be blessed (another sacramental) for Lent.
The color of the liturgical vestments is red, symbolizing the blood of the suffering Jesus. Red is used on Good Friday too.
"The passion of our Lord Jesus Christ guarantees our future glory. ... How can we weak human beings doubt that someday we will live with God when God has died for the sake of human beings?" (Sermon 218C, 1)