If WIS spells are coming from your faith/divinity, if you lose their favour, you might lose the spell (maybe temporarily)
That is just a proposal, but you can have a 10-Faith “loot” level, where you store WIS spells and a couple of Vows or Oaths or - something Vow of Poverty in the old DnD3.5
For example, the cleric starts selecting three oaths at character generation.
When they broke one, they lose access to three of their WIS spells. If all three are broken, they can’t cast at all.
Growing with power, they can get access to more powerful spells, but the oaths also might grow in number. So they are more restricted in their behaviour, as the divinity is looking at them more closely.
They can still lose them, but not for the attack of a viscous slime
I think it is quite simple, easy to remember, in the style of ICrpg - I guess - and it gets the feeling of old school clerics and divine power - again, I guess