Union of bodies is a sign of love but not necessarily love. "In married life itself, the conjugal act, which should be the most unique expression of married love and union, can in practice - unless there is extreme care and delicacy on the part of the spouses - become an act of one-sided egoistic possession rather than a love-act of mutual donation." Web Publishing of Cormak Burke, Mand and Values, Scepter Publishers, 2007, Ch. 10)
is a work of unification which goes far beyond the union of bodies. "The
body by its very physical nature is incommunicable. Two bodies cannot occupy the
same space at the same time. Animals never get inside of one another's mind by
mating, for there is no mind to penetrate. But there is something in a human that
is communicable and that can get inside of another personality, and that is his
mind, his attitudes, his ideals, and his moods." (Futon
J. Sheen, Three to Get Married, Society for the Propagation of the Faith,
1951, Ch. 10)
In marriage the union, man and women are meant to develop and understanding heart.
First, man and woman are different in their view and response toward reality. Woman due to her biological nature is closer to nature and also more aware of spiritual realities. She tends to sense intuitively the truth. Man on the other hand, tends to apprehend truth through logical reasoning. The world is to be studied and conquered. So, we hear at times men say that they do not understand women. The two complement each other and must be willing to listen to each other and modify their actions in accordance with the truth for the common good.
Second, each one has its own character traits due to genetic predisposition, family upbringing, education, developed convictions and idiosyncrasies, for better or for worse. Each has to learn to love the other even with its faults of character, that is, with an understanding heart, realizing that no one is free from negative qualities. Here they can complement each other. For example, one's husband may easily be inclined to anger, she can calm his anger by by her quiet attitude. One's wife may have a fearful attitude toward life events. He can dispel her fears by reassuring words. Marriage is a joint effort showing mutual respect filled with joy and pain leading to do God's will on earth as it is in heaven.
On the practical level, many suggestion are being made to promote unity in the areas of activities, intellect and will but when everything is said and done, "A few years of marriage is sufficient to teach us to what point the suffering lived by two people cements their union and how, by return to grace, this union helps them bear their suffering and offer it to God. Two weaknesses then become an astonishing strength. It is specifically in the common love of children that the union of hearts is established, just as it is especially in the maturity of later years that it will reach completion." (H. Caffarel, Editor, Marriage is Holy, Fides Publishers, Inc., Notre Dame, IN, 1957) pp, 56-57)