We've got to believe in something

we've got to believe in something is Disc 1, Track 3 on the Xenosaga III: Also Sprach Zarathustra Original Sound Best Tracks album. It has several variations, all from the music of A Missing Year: is a version without the main melody, and, , and  are all other variations.

It plays in the cutscene where the berserk Realians kill Febronia in the Old Church on Miltia.