From the Latin, meaning "by the work done." In sacramental theology, the objective reality and effectiveness of the sacraments when validly celebrated, regardless of the subjective attitudes or qualities of the ministers or recipients. For example, the real presence of Christ in the eucharist is not diminished by the lack of faith of one who receives the eucharist. Similarly, the validity of sacraments does not depend on the worthiness of the ministers. See Donatism.
Ex Opere Operato
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.