I have the same version of Anthems you have, I'm not sure what my favorite song is off there, either The Loss and Curse of Reverence or In Longing Spirit, I'll probably listen to Anthems in a couple months or so, it's really good, but to me Emperor went downhill from INTE, even though they managed to make great songs. I would've liked to see an album very similar to INTE right after it instead of Anthems, that and the synths and keys in INTE are better than in Anthems, though I like Ihsahn's vocals better on Anthems than onINTE.AFAIK, it was recorded for Anthems, but got switched out for another song last-minute, and placed on the "Reverence" single.
But doesn't matter to me; the version of Anthems I got, came with the Reverence single as bonus tracks; so I consider it part of the album. And I agree, great song; my favorite off of the album.