Sacred:Wounds Increase Damage Dealt

The Wounds Increase Damage Dealt: +XX% modifier found on some equipment amplifies the damage your character can inflict, ased upon the amount of injury you have received. The smaller percentage of full life your character has, the greater damage you will do.

Often, Drains own Life Energy (sometimes called Pain) and Life Leech will be used in conjunction with WIDD to amplify damage even more. This treatise on Adding WIDD to your Builds goes into much greater detail.