The idea that a marriage between a man and a woman requires a willingness to sacrifice for one another and expect nothing in return should be no surprise to anyone. Historically speaking, the exercise of natural marriage encompassed the human and spiritual compatibilities between a man and a woman. Each possesses a unique identity that exhibits a unified spiritual, moral, and sexual compatibility that presents natural marriage as a sacrificial gift of grace as ordered through the sacrament of holy matrimony and not a utility that can be used as one’s pleasure at the expense of the other.
When my wife and I first encountered the idea of sacrifice and the act of self-offering for one another as spiritual goods for a healthy marriage in our marriage preparation course, we were aware of the concept. Still, we needed help to come to a complete understanding of what that would maritally look like moving forward. As we developed a spiritual, moral, and pastoral awareness of one another, it became evident that our marital covenant must imitate Jesus Christ in sacrifice, love, and service to each other. Natural Family Planning became part of our moral and spiritual awareness of one another, and how it both challenged and strengthened our identity as husband and wife. If the basis of marriage is to love your spouse and the procreation of children, then it can be naturally argued that the premise of marital love is a natural self-giving of one another.
Natural marriage may be defined as the freely expressed union between a man and a woman for all eternity. The Son of God Jesus Christ made it a point to impress upon his followers, naysayers, and enemies, in particular the Sanhedrin, where He is the sole author of natural marriage now made visible as the sacrament of Holy Matrimony as expressed in his reference to divorce during the time of Moses. He also stressed the indissolubility of marriage, affirming that marriage was explicitly written in the human hearts of man and woman. God created man and woman’s marital compatibility to perpetuate God’s love for us.
The Catechism of the Catholic Church expands on the nature and identity of marriage as follows:
God, who created man out of love, also calls him to love—the fundamental and innate vocation of every human being. For man is made in the image and likeness of God, who is himself love. Since God created man and woman, their mutual love becomes an image of the absolute and unfailing love with which God loves man. It is good, very good, in the Creator’s eyes. And this love which God blesses is intended to be fruitful and to be realized in the common work of watching over creation: “And God blessed them, and God said to them: ‘Be fruitful and multiply, and fill the earth and subdue it.’ 
The Reasonableness of Human Sexuality
Human sexuality, if followed by God’s definition of marriage as mentioned in the Catechism, is reasonable in matter and form. Matter concerning the union of one man to one woman form the free self-offering in the act of matrimonial consent between spouses to love one another before the eyes of God and express their love through the gift of children.
The gift of sex between loving spouses I argue invokes a sense of faith, reason, and logic, but it expresses the mutual self-giving between spouses out of love for one another. Human sexuality is accurate and beautiful as ordered by God because of the intimacy expressed between man and woman in the sacrament of Marriage. Sex is reasonable because it compliments the affection and respect man and woman openly communicate toward one another in holy matrimony. The motive behind sexual intercourse between spouses is to affirm the gift of human sexuality given by God to man and woman. In the book of Genesis, we are reminded that:
God created man in his own image; in the image and likeness of God, he created him; male and female, he created them. And God blessed them, and God said to them, Be fruitful and multiply . . .
In The Truth and Meaning of Human Sexuality, written by the Pontifical Council on the Family, emphasized that man is called to love and self-giving in the unity of body and spirit.
Femininity and masculinity are complementary gifts through which human sexuality is an integrating part of the concrete capacity for love which God has inscribed in man and woman. Sexuality is a fundamental component of personality, one of its modes of being, of manifestation, of communicating with others, of feeling, of expressing and of living human love. This capacity for love as self-giving is thus "incarnated" in the nuptial meaning of the body, which bears the imprint of the person's masculinity and femininity. The human body, with its sex, and its masculinity and femininity, seen in the very mystery of creation, is not only a source of fruitfulness and procreation, as in the whole natural order, but includes right from the beginning the nuptial' attribute, that is, the capacity of expressing love: that love precisely in which the man-person becomes a gift and — by means of this gift — fulfills the very meaning of his being and existence. Every form of love will always bear this masculine and feminine character.
A contradiction in love?
Suppose the Church prescribes and teaches that the marital covenant comprises a sacrificial identity in Jesus Christ between spouses in holy matrimony. In that case, the continual proclamation of this marital covenant requires a sacrificial mindset toward your spouse without expecting anything in return. Concerning Natural Family Planning (NFP), the arguments against the practice range far and wide from practically every aisle of persuasion within the Church. The argument that NFP destroys a marriage because of abstinence from sex between spouses or that NFP is simply birth control in disguise often misses the purpose of why the Church affirms and teaches NFP.
The Catechism teaches that Natural Family Planning is part of man and woman’s cooperation with God’s love within the marital covenant.
A particular aspect of this responsibility concerns the regulation of procreation. For just reasons, spouses may wish to space the births of their children. They must ensure that their desire is not motivated by selfishness but is in conformity with the generosity appropriate to responsible parenthood. Moreover, they should conform their behavior to the objective criteria of morality.
Periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality. These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of authentic freedom. In contrast, “every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible” is intrinsically evil.
The premise behind the exercise of Natural Family Planning is not to destroy a man’s sex drive or to shatter any semblance of emotional intimacy between husband and wife. If a couple chooses to practice NFP and space the birth of future children for legitimate moral, spiritual and psychological reasons, it is done so with the understanding that both spouses are choosing to practice the virtue of abstinence in love for one another. It is not a permanent denial of sexual intercourse between spouses but a hopeful maturation in the mutual affection and affirmation of love for one another.