If Jesus was “going back” to God (as NIV mistranslates the Greek in John 16:28), he could not have been a human being, and Mary could not have borne the lineal descendant of David. And if Jesus was not the descendant of David, he could not have been the “son” of David and thus could not have been the Messiah (see Matt. 1:1 for his identity as the blood descendant of King David and of Abraham). The New Testament expects us to understand who Jesus is from its very first verse.
You cannot “be in existence” before you begin to exist. Therefore a so-called preexistent Jesus is an impossible idea.
Jesus, Gabriel announced to Mary, was to be known as the Son of God precisely because he was produced supernaturally by God in Mary’s womb — and for no other reason (Luke 1:35). That one reason is quite sufficient. Luke 1:35 provides the biblical reason for Jesus being the Son of God. He began to exist by miracle, and it happened in the womb of Mary, not before. Mary truly conceived a descendant of David, and God really became the father of a real son at the time of Mary’s conception. God had promised that He would in the future become the Father of the Messiah and this would have been untrue if God was already (in BC times) the Father of the Son! The Son of God was created in Mary by a biological miracle.
It is thus wrong to imagine Mary taking into herself an already existing Son of God (angel? or second member of a Trinity? or brother of Satan?). Matthew reports that Jesus came into existence “out of” Mary, by having his origin in Mary, and not outside of Mary. Mary was no surrogate mother, but the real biological ancestor of Jesus the Son of God, and thus older than the Son of God. Mothers are not younger than their sons! Jesus was not older than his mother. And Jesus was certainly not older than his ancestor David who lived a thousand years earlier than he.
For Jesus to be a member of the human race and not an angel or other sort of being, he had to come into existence, i.e., be begotten in his mother. All this was quite simple before the story became a hopeless tangle under the influence of post-biblical speculations. Matthew and Luke set out to report the facts about the “begetting” or genesis of Jesus, when and how it happened (Matt. 1:1: genesis; 1:18: genesis; 1:20: begetting in Mary).
To be “begotten” means that one is caused to come into existence. It cannot mean that an already existing Son is transformed into a different being, via his mother’s womb. That would not be a “begetting,” a bringing into existence, a beginning to be. It would be a transmutation or a transformation and all biological links with David or Abraham would be impossible. The real son of David was biologically and lineally related to his ancestors, and this would be out of the question if he was in fact older than his ancestors.
“Preexistence” is therefore a clever way of introducing a person other than the one Mary conceived and God begat in her womb. You cannot logically preexist yourself. The self who began in Mary is the true Son of God. A previously existing Son of God would be a different person and thus a different Jesus. If Jesus was alive before he began to exist, he did not really begin to exist. He did not begin to be, if he was already existing before conception and begetting. Thus a preexistent son actually rules out, cancels the actual Jesus who began “being” in his mother, as all human beings must. Preexistence is a subtle way of introducing a person other than the historical person whose mother was Mary. Mary of course conceived a real fetus who had to be, to qualify as Messiah, a blood relative via his mother of King David. At the same time, Jesus was God’s own Son, since Joseph was not the biological father of Jesus.The above article is taken from http://www.focusonthekingdom.org/99.htm#2