The full name of this day is "The Sunday of the Passion: Palm Sunday"
It is a day of contrasts. The Service begins with the Blessing of Palms, including the story of Jesus' entry into Jerusalem. Depending on the "All glory, laud, and honor," which has been sung on this day for centuries.
The readings for the day then turn to the Passion, the story of Jesus' last meal with the disciples, his arrest, trial, crucifixion and burial. The Passion Gospel is read in parts, with the people usually taking the place of the crowd. It is jarring to be shouting "Blessed be" one moment and several minutes later crying "Crucify."
The liturgical color of the day is a deep red, although sometimes the Palm Procession is done in purple, because it is still, technically Lent (until sundown on Maundy Thursday).
This is our longest Sunday Service of the year, but also one of our more engaging and rich ones. People rarely leave this Service unaffected by it.
Here's a brief reflection on the Passion by the Rt. Rev. Mariann Budde, the new Bishop of Washington, from her book, Gathering Up the Fragments:
"Holy Week is the time for us to experience and remember this most important of Christian truths: that when the lights go out and drakness reigns, when we are no longer able to rely on our own power and strength, God is there with a different kind of power, a different kind of strength. We often resist it because it requires surrender. It is the power of endurance and the gift of peace that can bring us through our greatest trials. Our sorrow is not eliminated but it is enfolded in God's love. Our suffering is not taken from us, but it is enveloped in God's light." (p. 136)