The parent-child relationship between God and human beings is the very axis of the universe, the most important of all relationships. It was this relationship that God created everything for.
According to Father and Mother Moon‘s teachings, God created us humans because of love. We are different from the rest of creation because we were created to be sons and daughters of God, and were meant to receive God’s love directly. This is the privilege of human beings. We are beings who are meant to respond to God’s love.
Father Moon explains the incredibly close relationship that should have existed from the beginning between God and us,

“Why did God need Adam and Eve? He had two purposes: first, to realize the ideal of love, and second, for the invisible God to make Himself visible after taking on a form. For this reason, Adam and Eve are the base and core through which the invisible God can assume a visible form and establish a relationship with the visible world.” (From a speech Sun Myung Moon gave 1st April 1977. Quoted from the English version of the speech collection Cheon Seong Gyeong, 2006-version, p. 95)
“What good would it be for the incorporeal God to remain apart from His creation? For God to remain invisible is of no use to Him. To be the Parent of human beings, God should be able to feel with a body as human beings do. For the purpose of assuming a body, it was necessary for God to create Adam and Eve as beings of dual structure, of mind and body.” (From a speech Sun Myung Moon gave 10th July 1984. Quoted from the English version of the speech collection Cheon Seong Gyeong, 2014-version, p. 85)
“Why did God create Adam and Eve? God is an incorporeal being, so unless He becomes the Parent in substantial form, He cannot directly love His children. Hence, He created them so He could have a form. Thus, the incorporeal God’s purpose in creating Adam and Eve was, first, to assume a form.” (From a speech Sun Myung Moon gave 6th July 1992. Quoted from the English version of the speech collection Cheon Seong Gyeong, 2014-version, p. 89)

We can perhaps best understand the relationship that originally should have existed between God and human beings, by looking at the relationship between God and Jesus. Jesus became what Adam should have become, an individual who was a living expression of the spirit of God. For that reason, Christian believers claim that Jesus was an incarnation of God, that God became human in a sense.
The Unification Principles emphasize that God is a fatherly and motherly being, with masculine and feminine aspects. And when God created human beings in his image, He created them as man and woman. Originally God should have become human through Adam and Eve in the Garden of Eden. Adam would become a living expression of God’s masculine characteristics, Eve of God’s feminine nature. For God to become completely one with human beings, there has to be a man and a woman. Thus, it follows that Jesus should have married, just like Adam and Eve should have been blessed in marriage by God, once they had grown up and matured sufficiently to become one with God in heart.
Unfortunately, Jesus was killed before he fully could show the path we are all meant to walk here on earth to become one with God. Therefore, the Messiah must return. When that happens, God and we may finally become one both here on earth and in the hereafter. As prophesied in the Bible,
“And I heard a loud voice from the throne saying, ‘Look! God’s dwelling-place is now among the people, and he will dwell with them. They will be his people, and God himself will be with them and be their God.’” (Rev 21;3, New International Version)