You touch a creature that has died within the last minute. That creature returns to life with 1 hit point. This spell can't return to life a creature that has died of old age, nor can it restore any missing body parts.
Because this spell is powered by necromantic energy instead of divine, the caster is drained of the HP it takes to get the subject to 1 HP, and must take a long rest before casting this spell again. This damage is reduced by one point per level of the caster above the level they can learn the spell, to a minimum of 1 point.
Example of use. Primrose the 5th level Necromancer's ally has fallen to -6 HP. When she Necromantically Revivifies him, she take 7 points of damage (1-7=-6). When she becomes an 11th level Necromancer the spell will only cause 1 HP of damage to her to revivify equal damage.
This spell is used by necromancers who don't want to do the "create and command undead" trope and instead want to become "healers" who want to discover "...the Secret...of Life...ITSELF!" (maniacal laughter at this statement optional).
* - (diamonds worth 300 gp, which the spell consumes)
Justification for Prim's Necromantic Revivify only causing damage "to bring the patient back to 1 hit point" to the caster when Life Transference does 4D8 to the caster.
The spell description for "Life Transference" is:
"You take 4d8 necrotic damage, which can’t be reduced in any way, and one creature of your choice that you can see within range regains a number of hit points equal to twice the necrotic damage you take."
So Life Transference is a 3rd Level spell, BUT it heals 8D8 to the patient. Cure Wounds would have to be cast as a 9th level spell to cure 8D8 (+1 D8 for every level above first). Other clerical spells increase the number of patients, but still need to be cast at higher levels to heal 8D8 to one patient. Prims Revivify is closer to the power level of other healing spells than Life Transference. And if someone has taken a LOT of damage (for example, dragon breath), the drain could be substantial to the caster.