Call to Worship in the Homeworld would cost Gems, and would give a set amount of belief at the Pit of Doom for each worshipper who comes.

Call to Sacrifice in the Homeworld would cost 1M belief and would be a good way to convert excess belief to Gems.

Both effects would be unlockable and upgradable. Upgrades would increase the area effect (distance followers can be called from) with the final upgrade unlocking calls from the entire map.

To implement something similar in Weyworld would require an equivalent to the Pit of Doom, but for now could be implemented with the Ark.