In this article on marriage, Fr. John Behr describes the historical shift in marriage from the pre-modern to the modern era and then explores the ascetical dimension of marriage beginning with the Old Testament, then on to the New Testament, and select writings of fathers of the Church, particularly St. Ireneaus, and St. Gregory of Nyssa.  He concludes that:

“Marriage is not simply about physical procreation of children.  That may happen if it is God’s will.  Rather, the challenge that Christianity brings to marriage, as it does also to the celibate life, is to undermine any confidence that we might play in either institution taken in itself, and to force us to look, instead, to Christ, to make Christ present in this world, spiritually to procreate Christ.  A Christian marriage is thus defined neither by its (possible) procreative function nor by its unitive function, nor even by both combined.  Each of these aims, taken in itself, is ultimately self-centered.  Rather Christian marriage is a means of manifesting Christ, continuing and extending his leitourgia and philanthropy (one part of which may be children).  And, in turn, marital asceticism as temporary sexual abstention is not simply the married couple’s brief taste of proper Christian existence, as if abstinence were in itself normative, nor is it, as it often becomes in modern thought on marriage, a means of making sexual activity, when it happens, more ‘unitive’.  Rather, temporary sexual abstention is a concession, as a God-given means of refocusing or redirecting our centre of attention, with the aim of achieving, finally, what was given from the beginning–to be males and females coming together in one flesh.  Perhaps, one may finally say, marriage is the arena where we finally come to be males and females in the image of God.  But the truth of this is still hidden with Christ in God, whose stature we have yet to attain.”