Forasmuch as each man is a part of the human race, and human nature is something social, and hath for a great and natural good, the power also of friendship; on this account God willed to create all men out of one, in order that they might be held in their society not only by likeness of kind, but also by bond of kindred. Therefore the first natural bond of human society is man and wife. Nor did God create these each by himself, and join them together as alien by birth: but He created the one out of the other, setting a sign also of the power of the union in the side, whence she was drawn, was formed. For they are joined one to another side by side, who walk together, and look together whither they walk. Then follows the connexion of fellowship in children, which is the one alone worthy fruit, not of the union of male and female, but of the sexual intercourse. For it were possible that there should exist in either sex, even without such intercourse, a certain friendly and true union of the one ruling, and the other obeying.
S. Augustine of Hippo, De bono coniug. 1.1
“The love of husband and wife is the force that welds society together. Men will take up arms and even sacrifice their lives for the sake of this love. St. Paul would not speak so earnestly about this subject without serious reason; why else would he say, “Wives, be subject to your husbands, as to the Lord?” Because when harmony prevails, the children are raised well, the household is kept in order, and neighbors, friends, and relatives praise the result. Great benefits, both of families and states, are thus produced. When it is otherwise, however, everything is thrown into confusion and turned upside-down.”
St. John Chrysostom, Homily 20 on Ephesians