From On Colossians, Homily 12. Translated by the Rev. J. Ashworth, 1879, and adapted by me. (This is from the Anglican series of Fathers translations that was pirated into the Ante-Nicene Fathers and other series.)
“[Marriage] is a mystery, and a type of a mighty thing… “This,” he says, “is a great mystery, but I speak concerning Christ and the Church.”
“…in our mysteries [ie, sacraments] there is silence and decency, modesty and bashfulness. A great mystery is being celebrated… How is it a mystery? They come together, and the two make one… At His entrance [in the Eucharist]… there is… great silence, great stillness. But when they come together, making not a lifeless image, nor yet the image of anything on earth, but of God Himself, and His likeness… they come, about to be made one body.
“See again — a mystery of love! If the two do not become one, they do not make many as long as they continue to be two. But when they come into oneness, then they make many. What do we learn from this? That the power of union is great.
“The wise counsel of God “in the beginning” divided one human into two, and He did not allow one to be enough of itself for procreation, being desirous of showing that, even after division, it still remains one. For one not yet joined is not one, but half of one. And it is evident from this: that he begets no offspring, as was also the case [with Adam] before [Eve].
“Do you see the mystery of marriage? He made one from one; and having made these two one, He makes another one by them, so that now also, a human is made out of one. For man and wife are not two humans, but one Human. And this may be confirmed… from the words, “He made them male and female.” …She was made from his side, and they are, as it were, two halves.
“…He sets their cohabitation ahead of both father and mother, to show that they are one. And in like manner, a father rejoices when either son or daughter marry, as though the body were hastening to join on its own member… though so great a charge and expenditure are incurred… Each one separately is imperfect for the procreation of children. Each one is imperfect as regards the constitution of this present life. Therefore the prophet [Malachi] also says, “The residue of thy spirit.” (Mal. 2:15, LXX.)