2Pce : Casting Inquisiton bathes you in holy light causing targets around you to take 6% additonal holy damage.
4pce CS / HoTR has a 50% chance to cause your TV / DS do deal an additional 100% weapon damage as Holy Damage to the primary target.
2 set allows greatly needed sustained dps and aoe dps and is a passive which i feel is important for tiers sets. Both should not be active effects you must track or things get far to clunky for the average player or even the world class player.
4 set allows the exact same damage to the boss if you choose to aoe or TV so you do not have to be afraid of breaking CC when AOE is not an option and when AOE is needed you can still get the benefit of the set bonus on a single target.