I'm personally interested in this topic as I am trying to learn what the Church or the Fathers teach about it. And I am here in good faith to learn.

The affirmation teaches us that the marital act is meant to '''“express their love in sexual union.”''' I believe that this is true and that this is the purpose of the marital act. However, if it is to “express” something then this implies that it is a symbolic act, a kind of language. Language is shared meaning. Language enables us to express our thoughts and feelings with others by employing symbols. Spoken language employs the symbols we call wordslocutions. In the marital act the bodies are speaking a “language” to one another. The loving union of husband and wife is the “meaning” that this language is meant to express. '''The primary question I am concerned with is whether or not a sexual act that intentionally rejects the very bodily and conjugal symbol of this love—namely the procreative power of the couples bodies—can still “express” the same thing—namely the union of love? Or does it actually express something different?'''

“The Theology of the Body”, which presents the church with a glorious vision of the meaning of Holy Matrimony and the purpose of marital intercourse, might shed light on this question. According to the “Theology of the Body” marital intercourse is not just sharing a touch or a sensation, not just one form of affection among others. Rather, as God designed it, marital intercourse is meant to be a true self-giving and the union of two selves without reserve. In this way it is the sharing of a power — an extraordinary, life-giving, creative, physical, sexual power. In the marital union, husband and wife are meant to experience the fullness of human vitality in its very source. And it is this procreative power that the couple share with each other that uniquely symbolizes and truly communicates the love and one-flesh union of a husband and wife. This By the "marital act" we are not speaking only of the biological configuration of bodies known as intercourse, but of the voluntary mutual self-giving and receiving (?perichoresis?) of that life-giving potential which is why the powerful expressive force that uniquely speaks of the bond they share. In other words this is not a kind of sexual mysticism but a creational theology of the meaning of down-to-earth matrimonial love. It explains how the two ends of marital intercourse — the procreative and the unitive — are linked together and why they cannot be separated.

By contrast, according to the Catholic “Theology of the Body,” in contraceptive sex no unique power is being shared except the power to produce pleasure, stripping the act of its true significance and ability to communicate. When the couple merely go through the motions of sexuality but reject each other’s fertility neither of them are giving themselves fully or accepting the other entirely. They are saying, "I want this genital feeling but I don't want to give you my fertility or receive your fertility. In this moment of intense intimacy I am holding back something and holding you back in a fundamental way." Contraceptive sex is an exercise in meaninglessness. The couple start to say one thing very beautiful with their bodies, something that speaks of love through the language of life. Then they deny that very thing in a refusal to fully know one another and nothing real is shared except sensation. By trying to found the uniqueness of marital oneness and express their love in an act of contradiction the spouses are haunted by the suspicion that their love making might be merely a false, hollow, selfish taking of pleasure.