In his encyclical Casti Connubii (On Christian Marriage), Pope Pius XII defined the foremost responsibility of husband and wife in marriage:
For all men of every condition, in whatever honorable walk of life they may be, can and ought to imitate that most perfect example of holiness placed before man by God, namely Christ Our Lord, and by God’s grace to arrive at the summit of perfection, as is proved by the example set us of many saints.
This mutual molding of husband and wife, this determined effort to perfect each other, can in a very real sense, as the Roman Catechism teaches, be said to be the chief reason and purpose of matrimony, provided matrimony be looked at not in the restricted sense as instituted for the proper conception and education of the child, but more widely as the blending of life as a whole and the mutual interchange and sharing thereof.[1]
Thus, the principle end of marriage is the mutual assistance of spouses in growing in holiness with the goal of reaching heaven.
Calling Couples to Christ 