Oath Binding

Excerpt from "Natural law and order, chapter 17- Power of the word":

Oath binding is something which can be done by any life form that can make decisions.

Basically, it is the voluntary decision to adhere to something. There is the need for a ritualized form that can be as simple as "On my word I'll be bound" to as elaborate as an oath of fealty.
Adherence is not enforced but knowing violations carry consequence.
Such consequences can be specified during the binding by the formula "...on my honour..." or "...shall strike me down..." and many others. If such a consequence is specified it will be met by the letter and by the intend via divine, arcane or natural power.
If no consequence is specified during the binding it becomes somewhat more ambiguous, consequences still occur but those are very much a question of "luck". Basically, whatever power can be deemed the relevant authority to the transgression will avenge it as it or they see fit. This could even mean several powers punishing the offender separately. Punishment is purely in the scope of the perceived severity of the transgression.

For example, a broken oath "on my honour" could result in a facial mark or in all people just knowing, that this person has no honour for a time or even permanently.
A broken loyalty oath with no specified consequence could result in a god of loyalty punishing you according to his law even if you are not even of his religion, but the offended party is. Simultaneously another power, god, magic etc could feel you need a bit more punishment and your own religion may also have things to say...
Quite often quests, pilgrimages or similar things are done to get rid of such punishments.