When the priest casts a raise dead spell, he can restore life to a creature. The length of time that the person has been dead is of importance, as the priest can raise persons dead only up to a certain limit.
Note that the body of the person must be whole, or otherwise missing parts are still missing when the person is brought back to life. Likewise, other ills, such as poison and disease, are not negated. The raised person is weak and helpless, needing a minimum of one full day of rest in bed for each day or fraction he was dead. The person regain their full health by natural healing or curative magic.
There is a reversed form of this spell, called slay living, which has the potential to immediately kill its target.
Note: This spell originally appeared in the 2nd Edition Player's Handbook for Advanced Dungeons & Dragons from TSR. Its use here is for the purposes of providing context for the campaign only.