Why do we do that? Catholic Traditions Explained

I read in the catechism that marriage is indissoluble. Why then does the church issue an annulment?

The description of marriage as indissoluble is found in several places in the Catechism of the Catholic Church. Described as required by spousal love (#1644) and as foundational to the union of marriage (#1646), this quality of marriage draws its meaning from the fidelity of Jesus to his church (#1647). Spouses give themselves once and forever to each other, forming a sacramental bond that binds them as one. Indissolubility presumes and depends upon the sacramental bond between spouses. An annulment does not destroy the bond. Instead, it shows that a sacramental bond never took place because, at the time of the vows, something was either present or absent that made the consent invalid. The ceremony itself does not bring about a sacrament, but rather the full, free, and able consent of a man and woman, one to the other. The husband and wife are the ministers of the sacrament to each other because they give the gift of themselves to one another. The priest is the official witness. Therefore, if the gift of self is not given, or is held back for any reason, no sacrament takes place.
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