The Primarch Lorgar didn't really spend 10,000 years sitting around, doing nothing much but write. In reality he went on quite a few pilgrimages to gain knowledge and inspiration. He would then return to Sicarus to write. The Primarch went out among the heathens on the fringes of Segmentum Obscurus around the time of the Angevin Crusade (he may also have gone there once before, in hallowed antiquity, but that's another story). This is know, for Castor has uncovered cults dedicated to Chaos and the Word on numerous worlds.

The priests of this faith are called Deacons of the Word, and they preach various variations over the same creed: Respect Chaos, placate the gods, Lorgar is the Man, his Sons are the avenging angels of the gods, they will help tear down the Imperium and build a new society. One built upon faith, and faith alone. Castor has integrated the Deacons with his fleet and host; the deacons are his priests among the mortal population. They are an important element in the infiltration work - without the prior existence of these cults the job of sneaking into Calixis would have been next to impossible (or at least much more difficult - and its already quite challenging!).