Jesuit On Celebacy

....the tension between the "debt" of marriage and the analogous "debt" owed by the priest. It is this tension which justifies the likening of priestly noncontinence to adultery. The latter debt, owed by the High Priest as Head of our fallen race, must be paid in persona Christi: it is the debt of the Cross, rendered to the benefit of the Church by the one High Priest, a ransom offered in his name, by his authority, at every celebration of the Mass. Here, it would seem, between the consummation of Matrimony by conjugal intercourse, and the consummation of the sacrifice of the Cross by the death of Christ, is the sacramental analogy we seek, and also the concrete transcendence of the symbolism of marriage by the symbolism of the Eucharist that is here in issue. It must be remembered that by both consummations, an irrevocable covenant is instituted, and that, as between these analogates, it is the Eucharist which constitutes the prime.

Link (here) to a fantastic piece by Fr. Donald J. Keefe, S.J. 
Priestly Celibacy in Patristics and in the history of the Church (here)