In the campaign I was runnning online for several years, the main religion WAS magic. The worshiped magic, the "Wizards Guilds" were "Magic Temples"
It then followed that those extremely dedicated to the religion were also the most powerful wizards. Players could pick any other religion and some had some divine intervention aspects to them, but nothing that scaled a priest of (insert religion here) to a mage-priest. There were also some wild magics used by non-followers of the religion, but there were no structured schools for that in most places, so you'd have to either teach yourself or return home to learn new things.