From Pope St. John Paul II’s Apostolic Exhortation Familiaris Consortio (1981):
God created man in His own image and likeness:20 calling him to existence through love, He called him at the same time for love.
God is love21 and in Himself He lives a mystery of personal loving communion. Creating the human race in His own image and continually keeping it in being, God inscribed in the humanity of man and woman the vocation, and thus the capacity and responsibility, of love and communion.22 Love is therefore the fundamental and innate vocation of every human being.
As an incarnate spirit, that is a soul which expresses itself in a body and a body informed by an immortal spirit, man is called to love in his unified totality. Love includes the human body, and the body is made a sharer in spiritual love.
Christian revelation recognizes two specific ways of realizing the vocation of the human person in its entirety, to love: marriage and virginity or celibacy. Either one is, in its own proper form, an actuation of the most profound truth of man, of his being “created in the image of God.”
Consequently, sexuality, by means of which man and woman give themselves to one another through the acts which are proper and exclusive to spouses, is by no means something purely biological, but concerns the innermost being of the human person as such. It is realized in a truly human way only if it is an integral part of the love by which a man and a woman commit themselves totally to one another until death. The total physical self-giving would be a lie if it were not the sign and fruit of a total personal self-giving, in which the whole person, including the temporal dimension, is present: if the person were to withhold something or reserve the possibility of deciding otherwise in the future, by this very fact he or she would not be giving totally.
This totality which is required by conjugal love also corresponds to the demands of responsible fertility. This fertility is directed to the generation of a human being, and so by its nature it surpasses the purely biological order and involves a whole series of personal values. For the harmonious growth of these values a persevering and unified contribution by both parents is necessary.
The only “place” in which this self-giving in its whole truth is made possible is marriage, the covenant of conjugal love freely and consciously chosen, whereby man and woman accept the intimate community of life and love willed by God Himself23 which only in this light manifests its true meaning. The institution of marriage is not an undue interference by society or authority, nor the extrinsic imposition of a form. Rather it is an interior requirement of the covenant of conjugal love which is publicly affirmed as unique and exclusive, in order to live in complete fidelity to the plan of God, the Creator. A person’s freedom, far from being restricted by this fidelity, is secured against every form of subjectivism or relativism and is made a sharer in creative Wisdom.
20 Cf. Gn 1: 26-27.
21 1 Jn 4: 8.
22 Cf. Pastoral Constitution on the Church in the Modern World Gaudium et spes, 12.
23 Ibid., 48.
— Familiaris Consortio 11