It's about the Protector of Mankind and his Legion.
The band in general is inpired by bands like Judas Priest and Manowar, which are huge on heavy badass battles.
It would be the second nerdy shout out on the album (with Necronomicon and Boden's peak, mentionned in Dance with the Devil)
They are "sending their ennemies to hell", [[ Literal Metaphor which would be literal in the 40k universe ]], and you have a mix of modern setting (the lights in the streets have gone out), a sense of destiny and long war ("All has led up to this moment"), and it can be used quite adequately in-universe as a [[ National Anthem pre-Horus Heresy anthem to the glory of the Emperor and the Primarchs ]].
