“1. On the basis of the doctrine contained in the Encyclical Humanae Vitae, we intend to trace an outline of conjugal spirituality. In the spiritual life of married couples the gifts of the Holy Spirit are at work, especially the gift of piety, that is, the gift of respect for what is a work of God.
This gift, together with love and chastity, helps to identify in the sum total of married life that act in which, at least potentially, the spousal meaning of the body is linked with the procreative meaning. It leads to understanding, among the possible manifestations of affection, the singular or rather the exceptional significance of that act: its dignity and the consequent serious responsibility connected with it. Therefore, the antithesis of conjugal spirituality is constituted, in a certain sense, by the subjective lack of this understanding which is linked to contraceptive practice and mentality. In addition to everything else, this does enormous harm from the point of view of man’s interior culture. The virtue of conjugal chastity, and still more the gift of respect for what comes from God, mold the couple’s spirituality to the purpose of protecting the particular dignity of this act, of this manifestation of affection. In it, the truth of the language of the body can be expressed only by safeguarding the procreative potential.”
via Respect for the Work of God.
from Theology of the Body
http://www.ewtn.com/library/PAPALDOC/JP2TBIND.HTM