I'm doing the (rather tedious) Spellforce tutorial to get to know the controls of the game. By now, I'm building up to destroy the second work camp and have build a Temple of Light, with an aria shrine next to it and another aria shrine next to the aria source.

However, when I want to create a cleric at my headquarters, the cleric's button is darkened and the help panel says: "Temple of Light - not in use". What's going on there? What should I do to be able to activate the temple and create clerics?

Just as you have to have a worker in the smith to produce any unit that uses iron,
so must you have a worker in the temple of light to produce clerics, and i think paladin.
If you take a close look at the temple of light, you can see a small slot meant for a prayer

ed: so take a worker from somewhere, and send it to temple of light as if you wanted to build the temple of light,
and that worker will occupy the slot

Thanks, that's the solution. It wasn't easy to get a worker in the proper slot, but after a few tries, I found out how to have the worker pray in the slot instead of just standing somewhere in the area of the temple. I guess my mistake yesterday was just seeing an idle worker standing, when in fact he was praying, and sending him elsewhere.

Thanks again.

A handy tip. If you select a building that takes workers, in the picture of the building in the bottom left (I think) there will be boxes representing the workers the building takes. If you click an empty box, it will put an idle worker in that slot.

A handy tip indeed. I just doubled your rep. by liking this post! Welcome to GOG.

*edit: or maybe I would have, if I had marked this topic as 'question'. I couldn't edit it to become a question-topic anymore post posting the first post (that's 3 posts in 1 sentence, but it's a correct sentence, not?). And two replies marked as 'answer' would be impossible anyway, I think (I never tried).

While on the subject i thought i should flash out another tip:
in case you want to speed up production/summoning of warriors,
build more maces/smiths/whatever buildings that are required,
when you have troll army you will feel the difference of having 1 vs 5 maces,
DE are also slow coming out of the monument.
Multiple food stores will likewise speed up mana & life regeneration