The Gift of Life is a process by which a Wraith can give its stored life energy to another. By doing so, they can heal that person of most injuries, whether they are Wraith or human. In humans, it will reverse the effects of the feeding process. They usually reserve it for only their "brothers" and most devout worshippers, though it can also be used to revive dead enemies for questioning. (SGA: "Common Ground", "Enemy at the Gate")
The Gift of Life can also be used to indoctrinate humans into worshipping the Wraith. By repeatedly feeding upon then restoring the life of the human, that person becomes open to suggestion, as well as dependent on the Wraith for continued survival. Humans deprived of Gift of Life go into severe withdrawal due to the lack of the Wraith enzyme in their system. (SGA: "Broken Ties")
According to the Wraith worshipper Dekaas, the Gift of Life can be used to extend a human lifespan, healing various injuries and ailments though there's some things even the Gift can't heal. Dekaas himself, a favored worshipper, was over three hundred years old, part of it spent in stasis but he spent a hundred and fifty years of linear time awake. Despite his actual age, Dekaas is shown to look between the ages of fifty and sixty. He tells Doctor Elizabeth Weir that this aspect of the Gift of Life is a highly kept secret amongst the worshippers. (Stargate Atlantis: The Third Path)
During her time trapped on an isolated planet, the young Wraith Queen Alabaster made a place for herself among the humans by sharing the Gift of Life on a small but regular basis, taking a portion of life from willing donors to sustain herself and using it to heal humans of birth defects and other serious injuries, such as taking fifteen years from an older man and using ten of those years to heal his newborn grandson of a fatal heart condition (Stargate Atlantis: Secrets).