indissolubility of marriage
"What God hath joined together, let no man put asunder" (Matthew 19).
When the sacrament of matrimony has been received by a man and a woman and ratified by their cohabitation as husband and wife, their union cannot be dissolved except by death.
Protestants often quote those other words of Christ in the same chapter, "Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery"; but it is plain that this permits not a divorce but a separation.
It is not a dissolution of the marriage bond, but a putting away of the guilty party; for elsewhere our Lord declares that "He that marrieth her that is put away from her husband committeth adultery" (Luke 16).
Saint Paul commands that the wife shall not depart from her husband, "and if she depart, that she remain unmarried, or be reconciled with her husband" (1 Corinthians 7).
Here there is a distinction between the mere contract of marriage and the sacrament of matrimony.
The Church, for grave reasons, can dissolve the contract of marriage when the sacrament has not been received, as explained in the article on the Pauline Privilege, but when the sacrament has been received and has been ratified by marital cohabitation, marriage cannot be and never has been dissolved.
Because the Catholic Church enforced this law, schism and subsequent heresy invaded one of her choicest realms when a pope refused to grant a divorce to a licentious English king.
New Catholic Dictionary