[New setting] How does magic inform a setting?

Right, I will finish the review soon, but I have had a game thought in my head. So I am putting this down before I lose it.

I am writing the setting such that every single person has real, demonstrable magic. This means it is going to have a huge effect on the setting, surely? So I need to be thinking about how this will effect groups.

First of all, it seems to me a lot of cultures in the ancient world were defined by how much was needed to feed everyone. When it takes 900 calories to grow 1000 calories of food, then everyone will be spending a lot of time farming. In fact, I have often wondered in fantasy settings where bad shit is out there all the time how enough farming happened to feed everyone.

Imagine if this worked and was key to good yields?

So, farmers have farmer magic, sheepherders have sheepherder magic. This makes them nebulously better at their jobs. This should surely result in their being more food to go around. More food means more specialists. That means that there is then more people who can do odd jobs in the society.

But because someone gets magic related to their professions. there will surely be a greater deal of stratification in society. Someone born as a noble will have noble magic and be good at it. Someone trying to join that caste will have to initiate again, presumably at some great cost. But then people went through expensive rituals to gain in social class in the real world.

Also, I imagine there will be a lot more priests as the power of the gods is demonstrable and powerful in the setting. I suspect that there will be a lot of priests taking up some of that food surplus, working on the miracles and powers of their respective deities.

Imagine if this fucker could cure disease with a touch (and an elaborate ritual). 

How may would Egypt have supported?

So, there is more food going about, terrible social mobility and more priests going about doing priestly things. So, what are those priest things? 

Well, sickness would be less of a thing, presuming there is a god of health or sickness. It seems unlikely that there would not be, too. Presumably there would also be a grain/farming/herding god or goddess for each culture. Supporting a priest might not improve yields, but maybe it staves off or lowers the chance of bad harvests and famine? If so, a security of harvest would have an enormous effect on the world in the iron and bronze ages. What exactly seems to be something I need to research a little more.

Taxation and magic taxation

So, taxing is hard. You need an organised state to have a good idea of who you can tax, and you need to be able to trust someone to go and get money or goods and then give it to you. Taxation is hard. It upsets people and lots of times and places have found it something that is nearly impossible to do properly. So, add to this that in this setting people can be expected to send their magic to other beings, up to and including the sorcerer demigod who rules your kingdom and you have to be able to organise worship and ritual across diverse areas, probably against people's own best interests (they could use that magic!) .

Certainly, I suspect that this isn't something that disorganized tribes of hunters or pastorals are able to put together. So, you might find that the organised city based states tend to be the ones who attract a powerful being as a ruler or patron. Also as they can manage more money and surplus for elaborate temples they might end up with more of the avatars and aspects of the settings gods in them as well. 

From this I see organised empires, headed by powerful beings making incursions on hill tribes and suchlike who have a much higher proportion of people who have been initiated as warriors or raiders, and hence are much fiercer personal combatants. However the empire has more wealth to bring to bear, and hence ends up with more priests blessing their soldiers and a much better chance of a semi-divine being influencing the field. I could see that being a fun conflict. More later as I think about it.