Marriage was divinely established in Eden and affirmed by Jesus to be a lifelong union between a man and a woman in loving companionship.
They were His finale, the best of the exceedingly good gifts He gave humanity at Creation.
The act of sexual intimacy is the nearest thing to a physical union possible for them; it represents the closeness the couple can know emotionally and spiritually as well.
Christian married love should be characterized by warmth, joy, and delight (Prov. "Marriage is honorable among all, and the bed undefiled" (Heb. "The Scriptures tell us clearly that the joyous sexual expression of love between husband and wife is God's plan.
"But for Adam there was not found a helper comparable to him" (Gen. God was sensitive to this lack, for He said, "'It is not good that man should be alone; I will make him a helper comparable to him'" (Gen. The Hebrew word neged, translated "comparable" here, is a noun related to the preposition that means to stand "before, in front of, opposite, corresponding to" someone or something.
In this case the person who was to stand in front of Adam was to complement him, corresponding to him as his counterpart.
It is, as the writer of Hebrews emphasizes, undefiled, not sinful, not soiled.