Vows are faith based sworn words which commit the swearer to act in such a way as proscribed by the tenets of the Principle or Institution. These create a strong bond between a powerful entity and those that serve. Breaking such a bond imposes retribution from the entity’s powers and authorities. These are most often penalizing them in a multitude of ways, but is ultimately be dictated by those who had the bond to them broken (an act of defined Transgression).
This is, in essence, a vow but made by characters not part of a faith, but openly witnessed and empowered by the divine Principle which they have called upon. In return for minor divine favor and favorable disposition from religious authorities (if any), they must keep their bond. To break such a bond without a cleansing and mutual feelings threatens the permanent measure of Sanity a character may possess.
Implementing these ideas can provide for a myriad of game facets: