The Church teaches that a valid marriage bond is indissoluble, that is, it’s unable to be broken: “The love of the spouses requires, of its very nature, the unity and indissolubility of the spouses’ community of persons, which embraces their entire life: ‘so they are no longer two, but one flesh'” (CCC, no. 1644). In today’s Sunday Pope Quote, Pope Pius XII gives a beautiful word-picture of what indissolubility does and why it is a gift and a blessing.
Pope Pius XII: In the face of such a law of indissolubility, human passion in every age, chained and repressed in the free satisfaction of its inordinate appetites, has sought in every way to throw off its yoke. Passion sees in this law only a hard tyranny, arbitrarily weighing down conscience with an unsupportable burden, with a slavery repugnant to the sacred rights of the human person. It is true; a bond can at times constitute a burden, a slavery, like the chains which bind the prisoner. But it can also be a powerful aid and a sure guarantee, like the rope which binds the alpine climber to his companion during the ascent, or the ligaments which unite the parts of the human body, making its movements free and easy. This is clearly the case with the indissoluble bond of marriage” (emphasis added).
– Audience with newlywed couples on April 22, 1942, from Dear Newlyweds: Pope Pius XII Speaks to Married Couples, trans. James F. Murray Jr. and Bianca M. Murray (Kansas City, MO: Sarto House, 1961), p. 88.