[Saulot]

Pretenders automatically spread dominion (you could consider it preaching, for free). It's on pg 92 of the manual.

Click on a temple in game to see what's spreading dominion, and by how much.

Also, since we're talking about a lvl 6 priest, he could raise to a theoretical maximum of lvl 12 dominion (13 with a temple). Though 10 is the actual limit of dominion.

Edit:

Offhand, the best comparison is probably another immortal, living pretender, a "Bakemono Kunshu" (unit 1428).