The final Sunday of Lent, which also serves as the beginning of Holy Week is called Palm Sunday of the Passion of the Lord. On this day, the Catholic Church celebrates the triumphant entry of Jesus into Jerusalem, days before his passion and death on the cross.
In the Gospels, Jesus enters Jerusalem riding a donkey. Paying homage by spreading cloaks and leafy branches on the road, the people welcomed Jesus. This scene of Jesus’ arrival in Jerusalem is being reenacted in the Holy Masses annually on Palm Sunday. The faithful bring palm fronds which they use to participate in this reenactment. Recognized as a symbol of peace and victory, palm branches are preferred to be used on Palm Sunday.
In Holy Masses, mass goers carry palms in the procession during the celebration. The palms which are also blessed are then reverently kept by the faithful in their homes throughout the year. In the following year, these blessed palms are then brought to the church to be incinerated and made ashes for Ash Wednesday.
Also called Passion Sunday, the Holy Mass also commemorates the passion of Jesus as the Gospel narrates His suffering and death on the Cross. The use of the colors red and white on the Mass symbolizes the salvation of mankind from sins through the blood of Christ.
Palm Sunday: https://www.catholic.org/lent/palmsunday.php