I watched that scene again, and the quote was:
And Saint Attila raised the hand grenade up on high, saying, 'O Lord, bless this Thy hand grenade that, with it, Thou mayest blow Thine enemies to tiny bits in Thy mercy.'
So, in this context,
thou is appropriate. But... what about the one in the Holy Seal flavour text? Should it be
thou or
ye?