If you aren't familiar with the entirety of Handel's Messiah, it is done in three parts and is about (as you might imagine) Jesus Christ as Messiah. It's often performed at Christmas, but sometimes at Easter as well. Seeing it at Avery Fisher Hall, Lincoln Center, was a real treat. Part 1 is about the prophecies before Christ's birth and ends with the Annunciation; Part 2 is about the Passion of Christ and ends with the much-beloved Hallelujah chorus. Part 3 is about the resurrection and rebirth of Christ.
In the picture below, the entire chorus is standing for the Hallelujah chorus, including additional choir members who are present only for that one part, seen in the second picture in two levels of the balconies. It truly sounds like the heavens have opened up and a choir of angels is singing when you hear this performed live at Lincoln Center.