Well, here's an interesting article. Looking for the Kingdom Come: Questioning Spirituality in U2. It's from Popular Musicology Online and dates to 2002 though strangely takes no notice at all of ATYCLB. He talks not only about U2's lyrics as "spiritual" (whatever that means) but also about why their music has a spiritual effect, first dealing with their early work...

...simple harmonic patterns (without extended verse-refrain forms), a driving bass technique, busy and echoic guitar patterns in high register, and a recitative-like vocal approach; the combination of these seems to cry out the band's sincerity. The epic, ideologically sound nature of many songs from the 1980s, the band's evident devotion to its audience, and three of the members' reasoned Christian commitment confirmed their idiolect's connotations ...U2's idiolect up to the late 1980s (as far as "Rattle and Hum," in fact) affords the listener a centring experience, the provision of an existential authenticity, an experience to be trusted....

...and then rebutting arguments that 90s U2 was about something else. On later albums, that spirituality is not overturned, is not found wanting. It remains present, but is presented even more elliptically, as if to acknowledge that the only way to encounter the subversions of secular postmodernity is to subvert those. He has some interesting stuff on ZooTV, and a take I never heard before on "The First Time":

The refrain asserts that "for the first time, I feel loved". The last of three verses focuses on a 'Father', owner of many mansions, but Bono 'left by the back door' and 'threw away the key'. Having repeatedly rid himself of this idolatrous object, however, the song intimately closes with the refrain.

Hm!