Emissary of Purity

Your Emissary of Redemption ability is enhanced, embodying the Pureness of the heart, body, and soul, as the holy trinity you are the way.

• The damage resistance cannot be negated or ignored.
• Your ability resets on a target if you have taken no other actions against a creature in the past round but offer peace.
• Creatures that deal damage to you (including damage from Aura of the Guardian) take radiant damage equal to the damage you take from the source replacing the ability that does damage.

Reference

Emissary of Redemption
At 20th level, you become an avatar of peace, which gives you two benefits:
You have resistance to all damage dealt by other creatures (their attacks, spells, and other effects).
Whenever a creature hits you with an attack, it takes radiant damage equal to half the damage you take from the attack.
If you attack a creature, cast a spell on it, or deal damage to it by any means but this feature, neither benefit works against that creature until you finish a long rest.