It refers to the myth (or Biblical truth, depending on your perspective), of Lucifer’s fall from heaven and this concept that he will rise again with an army of followers to destroy Michael the Archangel and his army. Like a second war in heaven but this time Lucifer will be victorious. That is, referring to the supposed events in heaven that are described in the Book of Revelation and the Apocryphal texts, but with a different outcome. I don’t think Davey is referring to it in a truly religious sense, but rather a metaphorical one; the rejected and downtrodden will rise above the “normal” and acceptable in due time.
This is really obvious in certain lines:
I’ve accepted silently this name that I’ve been given. That is, the name Satan, which meant “adversary”, and is not Lucifer’s true name (which means “lighter-bearer”)
Now hand to hand my voice shall be heard. Which sounds like a direct reference to the supposed battle between Lucifer and Michael (hand to hand, i.e. swords).
There’s actually a shit-ton of Judaeo-Christian references in his lyrics. Especially about Lucifer, the fallen angels and the watchers, etc. I think it’s really fascinating and beautiful and it really fits the music conceptually.
Edit: Davey refers to Lucifer a lot, especially on The Art of Drowning. The title Morningstar is taken from another name for Lucifer, as he was referred to as “the morningstar”, because in ancient times he was associated with the planet Venus and before he rebelled against God, he was the brightest and most beloved of God’s archangels. Davey also talks about “falling” a lot in these lyrics that also have a biblical narrative to them, which makes me believe the entire myth of Lucifer was very influential to him, but I think he uses it in a little bit different way. Not in like a LaVeyan way, but perhaps as a metaphor for being hated and rejected and scapegoated for being different,. This occurs in The Lost Souls and The Nephilim as well (the Nephilim were supposedly a mixed race of half human, half angel). If I take a few moments to flip through The Art of Drowning and to a lesser extent, Black Sails, I’m sure I can find a lot more.
Sorry for the word vomit, I’m kind of obsessed with Western esotericism.