The logic of this process in England was amazing. You would swear before God that your claim was true, and so would your opponent. And then God would favour the honest claim.

But then people realized you could have someone fight for you if they'd swear that your claim was true (IE, they'd be a witness). If you lost the duel, it would mean that you lied, making it perjury. So your equivalent of a lawyer would be some renowned fighter, undefeated in combat (since if you were defeated, you wouldn't be able to swear in as a witness).

It turned into situation where you'd use the person you hired as a negotiation tool (oh you hired "Bob the Barbarian" as your champion? Let's settle 60/40), so most challenges wouldn't even come down to a fight.