I dont understand the point of this spell?

Lets see.In the best possibly scenarios a temple regent spends 1 GB and 1 RP to increase his temple holding by 1 level.This nets a gain of 1 RP and 2/3rd GB.

The owner of hte province(usually,but not always someone else) also benefits,to the tune of 1 GB and 1 RP for the increase in province level.

Thus in most cases the temple regent loses 1/3rd GB for performing the spell, as well as the standard action required.

So, to benefit from this action the temple regent must make some kind of agreement with the province ruler, that the province ruler must pay part of the casting costs.Lets say 0.5 GB/0.5 RP for example.

This nets the temple regent about 0.1 GB(estimation) and 0.5 RP profit, and the province ruler gets 0.5 GB/0.5 RP.

Hardly worth the cost of a standard action IMHO.