late 14c. (mid-13c. as a surname), "shepherd, one who has care of a flock or herd" (a sense now obsolete), also figurative, "spiritual guide, shepherd of souls, a Christian minister or clergyman," from Old French pastor, pastur "herdsman, shepherd" (12c.) and directly from Latin pastor "shepherd," from pastus, past participle of pascere "to lead to pasture, set to grazing, cause to eat," from PIE root *pa- "to feed; tend, guard, protect." Compare pasture.
The spiritual sense was in Church Latin (e.g. Gregory's "Cura Pastoralis"). The verb in the Christian sense is from 1872.