In so doing, the Word Bearers tied up the single biggest Legion at a time when it was most needed.
When the Warmaster's armies closed upon Terra, the Ultramarines were thousands of light years away and unable to intervene until events were all but decided.
The Emperor, who the Primarch had counted a god, had denounced his own divinity, denying the tenets of the faith in which Lorgar had been raised.
Confronted by the possibility that the Word was false, Lorgar may have sought other meanings within it, and other beings that might serve in the place of the god he had believed in.
Today they bend all their considerable efforts towards the overthrow of the "Corpse Emperor" in the Long War and spreading the "truth" of Chaos to all Mankind.