Why does Roman Catholic teaching say that a minister’s personal virtue does not determine whether a sacrament is effective?

In Roman Catholic theology, the effectiveness of a sacrament is understood through the principle of ex opere operato, a Latin phrase meaning "from the work done". This teaching holds that the virtue or personal holiness of the minister does not influence the validity or efficacy of the sacrament.12

The rationale for this doctrine is that the minister acts merely as an agent of the church, while the true effectiveness of the sacrament is derived from the saving act of God in Christ. Because the sacrament is an outward sign instituted by Jesus Christ, its power is not dependent on the human qualities of the person performing the rite. If the minister’s personal state were a requirement for validity, it would introduce uncertainty into the sacramental life of the church, as the recipient could never be certain of the minister's spiritual condition. By focusing on the objective action of the rite itself, the church ensures that the grace conveyed is rooted in the promise of God rather than the merit of the individual minister.2