Wikia

Divine Purpose
Divine Purpose (Passive) Passive Abilities that cost Holy Power have a 25% chance to cause the Divine Purpose effect. Divine Purpose Your next Holy Power ability will consume no Holy Power and will cast as if 3 Holy Power were consumed. Lasts 8 sec.
Usable by
Class	Paladin
Properties
School	Physical
Talents
Talented	Yes
Level required	75
Related buff
Divine Purpose Your next Holy Power ability will consume no Holy Power and will cast as if 3 Holy Power were consumed. Duration: 8 seconds

Divine Purpose is a passive paladin talent available at level 75.

Patch changes

Patch 5.0.4 (28 August 2012): Updated.
Patch 4.0.6 (8-Feb-2011): The chance for applicable abilities to generate Holy Power has been reduced to 7/15%, down from 20/40%, but instead of generating 1 Holy Power, the next applicable ability used consumes no Holy Power and acts as if the paladin has 3 Holy Power.
Patch 3.1.0 (14-Apr-2009): Moved to Improved Retribution Aura’s position.
Patch 3.0.3 (04-Nov-2008): Rank 1 of this ability will now correctly determine its chance of remove stun.
/ Patch 3.0.2 (14-Oct-2008): Divine Purpose (Retribution) now reduces chance to be hit by spells and ranged attacks by 1/2/3%.