Today is Palm Sunday, when we commemorate Christ's triumphal entry into Jerusalem. The below video gives one of the Gregorian Chant Antiphons for the Palm Sunday procession. Here is the text: Hosanna filio David; benedictus qui venit in nomine Domini. Rex Israel: Hosanna in excelsis. (English translation: Hosanna to the Son of David; blessed is he who comes in the name of the Lord, the King of Israel. Hosanna in the highest.)
And here are some wonderful pieces of sacred art to view as you listen to the antiphon.