Of Kings and Men
The way Magic works is a little changed. All magic, be it divine or arcane, originates in the Gods and Ancients who bestow spells and magical power upon their worshipers.
A caster character is advised to worship their chosen deities occasionally by sacrificing something their God likes and pray to him. (This is more RP-oriented, rather than mechanically.)
It is required that the player specifies that he does so.
If a caster does not pay heed to his chosen God or the Ancients, there will be consequences – his spells might weaken or he might find himself unable to cast as many spells per day, as he is not granted as much power as he usually has.