Marriage, objectively considered, must provide first of all the means of continuing existence, secondly a conjugal life for man and woman, and thirdly a legitimate orientation for desire. (p. 66)
The Church, in arranging the objective purposes of love in a particular order, seeks to emphasize that procreation is objectively, ontologically, a more important purpose than that man and woman should live together, complement each other and support each other, just as this second purpose is in turn more important than the appeasement of natural desire. But there is no question of opposing love to procreation nor yet of suggesting that procreation takes precedence over love. These aims can, moreover, only be realized in practice as a single complex aim. (p. 68)
Those who cut themselves off absolutely from the natural results of conjugal intercourse ruin the spontaneity and depth of their experiences, especially if artificial means are used to this end. Lack of mutual understanding, and of rational concern for the full well-being of a partner, leads if anything still more certainly to the same result. (p. 69)
—from Love and Responsibility by Karol Wojtyla (Saint John Paul II)
—The 30 page document John Paul II on Love and Responsibility is a good introduction to the book Love and Responsibility. It is mostly made up of excerpts from the book, but it also includes excerpts from other official and personal writings on love by Saint John Paul II.