The Use of the Word Knew in Scripture
by Father Chris Pietraszko

Why does scripture use the term, "knew" when describing a sexual relationship? (i.e. Gen 4:1)
Sexual Relationships ought to go much deeper than simply a carnal experience. Rather, the depth of a sexual encounter ought to bring about an awareness of the Other that leads to an inter-subjectivity between the spouses.
Inter-subjectivity is where the soul of the two individuals has a common-sharing in each other, and they can begin to experience love through the other's own spirit. The two become one. As they develop an awareness and appreciation of the other, their own spirit becomes intertwined with the concerns and will of the other, like two interlocking mechanisms which depend on each other for their own purposes.
Knowledge thereby differentiates the sexual act of two human persons from two beasts (animals).
Therefore, without this deep, inter-subjectivity between spouses during the act of sexual intercourse, each human being acts towards the other as if they are merely an animal. This is why many end up feeling used and empty after a sexual relationship that was purely for entertainment, pleasure, or with regards to the self.
Without the inter-penetration of personal knowledge of the other in this act of intercourse, men and women treat themselves and each other as less than what they truly are. As a result, at the very core of our dignity, which has been suppressed, the human person becomes wounded by such a gravely immoral act, which falsely communicates that man and woman are no more important than dogs breeding. An act which ought to express the dignity of the other is degraded to something base, and the most precious aspect of the other is trampled under foot.