The Lunatic Cultist description explains he is trying to bring back Cthulhu, the Moon Lord, to end the world through various forms of scheming and plotting.

They are literally holding back the Moon Lord. It would make sense for the Terrarian to literally summon a god just to kill it. After all, why the fuck did he fight the WoF, Skeletron, Empress of Light?

I thought Red said that they were trying to contain the Moonlord, hence the reason why the celestial pillars spawn right after killing Lunatic Cultist... because the player essentially broke the barrier.

Alright then why would the player come kill the cultists?

their trying to keep moon lord form coming back wdym

It would make no sense for the player just to come barging in and kill the cultists only to screw themselves over and be faced with the Lunar Pillars and Moon Lord afterwards because the cultists were keeping him at bay the whole time. It seems more likely that the cultists want to bring Moon Lord back, but you come in while they are doing their ritual, and rightfully piss off their boss, who calls in the Moon upon defeat as a last resort.

think their tryna seal him actually

Yes, in lore they are trying to summon him.

Pretty sure in the lore it says they are trying to bring back Cthulhu

i love the pack tho

they r not worshiping it, they r trying to stop it from getting to earth, and the pillars r the last line of defense. "You either die a hero, or live long enough to see yourself become the villain."