Ordination. The setting apart of some members by a church for ministerial or priestly leadership, usually by laying on of hands and invocation of the Holy Spirit. It is considered a sacrament in Catholic and Eastern Orthodox theology. Ordination usually requires both a spiritual call from God and an ecclesiastical call, including the fulfillment of standards of training, doctrinal conformity and other institutional requirements. Most churches require those who administer the sacraments or ordinances