Source is connected with magic the way I understand the lore but using normal spells only need your own mental strenght. While source spells use the source energy itself. So the collars just prevent you to use source energy.
All spells require source. Without source it's impossible to cast any spell
Where is everyone replying getting the idea that there are 2 different spell types
There are no such spells in the divinity universe labeled as "SOURCE SPELL" nor is there any spell in the entire divinity universe that says "REQUIRES SOURCE"
There is also no such thing as "SOURCE MAGIC" and regular MAGIC"
As I said read the lore and you will find that Source is what everyone knows in general terms as MANA. it is the SOURCE of being able to cast spells..Hence the word SOURCE.
