With each level of this Perk, you gain an additional 4 Hit Points. This may not seem like a lot, but every little bit helps.
Livegiver or Life Giver is a perk in Fallout.
+4 hit points per level gained (+8 with both ranks). The gain is quite substantial and with both ranks effectively doubles the HP gain at 10 Endurance could give (8 from the perk and 7 from the stat), giving an excellent margin for any heavy fighting and criticals. Even a single rank is a substantial bonus.
Behind the scenes
The image and title of this perk is a Vault Boy presented in a manner consistent with representations of Jesus Christ.