This does not eliminate the need for church involvement in the marriage; under normal circumstances, canon law requires for validity the attendance of the local bishop or parish priest (or a priest or deacon delegated by either of them) and at least two witnesses. The priest has merely the role to "assist" the spouses in order to ensure that the marriage is contracted in accord with canon law, and is supposed to attend whenever it is possible. A competent layperson may be delegated by the Church, or may just attend in place of the priest, if it is impractical to have a priest attending. In the event that no competent layperson is found, the marriage is valid even if done in the presence of two witnesses alone. For example, in May 2017, the Congregation for Divine Worship and the Discipline of the Sacraments granted a bishop's request that a nun be granted permission to officiate at a marriage ceremony in Quebec because of a shortage of priests. Eastern Catholic churches share the tradition common throughout Eastern Christianity, according to which the minister of the sacrament is the bishop or priest who "crowns the bridegroom and the bride as a sign of the marriage covenant", a ceremony that has led to the sacrament being called the Crowning. Catholic theology teaches that a validly contracted sacramental marriage is accompanied by divine ratification, creating a virtually indissoluble union until the couple consummate, after which the sacramental marriage is dissoluble only by the death of a spouse. An unconsummated marriage can be dissolved by the Pope, as Vicar of Christ. Once a sacramental marriage is consummated, only a separation is possible: the marriage bond cannot be dissolved by any power. In the eyes of the Church, even validly contracted natural marriages (marriages in which at least one of the parties is not baptized) cannot be dissolved by the will of the couple or by any action of the state. Accordingly, "the Catholic Church does not recognize or endorse civil divorce of a natural marriage, as of a sacramental marriage". However, a natural marriage, even if consummated, can be dissolved by the Church when to do so favours the maintenance of the faith on the part of a Christian, cases of what has been called Pauline privilege and Petrine privilege. In these cases, which require intervention by the Holy See, the Church admits real divorce, actual dissolution of a valid marriage, as distinct from the granting by merely human power of a divorce that, according to Catholic theology, does not really dissolve the marriage bond.