Summary: John begins his examination of the ministry of Jesus by looking at the Incarnation. The message seeks to explore what this means for believers.
“The Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.” 
One can focus on minutiae and fail to see the beauty presented in the story of God’s love. Nevertheless, for a moment think of separating the Christmas story into component parts. If you could place the Christmas event in a test tube, testing its reaction as in a laboratory, what would you discover? If you could dissect this holy season, exposing each component part for careful and minute scrutiny, what do you suppose you would learn?
We are given a perfect revelation of the Living God in the Christian celebration of Christmas; and few writers have done more to reveal the essence of Christmas than has the disciple whom Jesus loved. Though we are not prone to think of John as one of the Scripture writers who provided a detailed account of the advent of our Lord, he nevertheless made a significant contribution to our understanding of that holy event. John details the heart of Christmas in the opening verses of his Gospel. In particular, the verse serving as our text is decidedly a Christmas text which has too long been neglected by both pulpit and pew.
I said I wanted to segregate the Christmas story into component parts in order to examine them; I suggest this with some trepidation. Separating the account in order to understand is fraught with danger if we lose balance. The Word of God presents Jesus as unique—He is fully God, and He is fully man. This presentation of the unique God-Man is almost universally rejected. While we would anticipate that those enmeshed in recognised cults would reject this truth, we are always somewhat startled when we learn that professing Christians reject this truth.
Two significant heresies plaguing the early churches were Docetism and Nestorianism. Tragically, these heresies are still resident among the churches in this day, as problematic as ever despite being answered and rejected soon after they arose. Docetism, among other similar teachings, taught that Jesus is fully God. However, they reject the biblical teaching that He was truly and fully man. Docetism, the term is derived from the Greek term dokéo, meaning “to seem” or “to believe,” denied the Incarnation of Jesus. Generally, Docetism taught that Jesus only appeared to have a body. The teaching arose out of the supposition that follows dualism, that the body is inherently evil. Thus, according to this view, God could not take on human flesh as the body is evil and God cannot be associated with evil.
Our text puts the lie to this ancient heresy when John writes, “The Word became flesh and dwelt among us” [JOHN 1:14]. The case for Christ’s presence in human flesh is made strong still when John writes in his first letter, “By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God” [1 JOHN 4:2, 3]. For the sake of completeness, consider one other statement which John provides believers. Writing in his second letter, John testifies, “Many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist” [2 JOHN 7]. Any teaching that denies Jesus was fully man, or even that depreciates the importance of His humanity, must be considered docetic. God Himself identified with fallen mankind, sacrificing Himself for us.
Nestorianism is similar to Docetism in that it holds that Jesus is two distinct persons. Nestorianism, named after Nestorius, who served as Patriarch of Constantinople in the Fifth Century A.D. Because of his error, Nestorius was deposed as Patriarch and sent first to Antioch, then to Arabia and finally to Egypt. Though Nestorianism originated in response to the designation of Mary as “Mother of God,” the heart of the argument Nestorius advance denied that Jesus was very God. Nestorius held that the Christ had two distinct, though loosely associated natures—human and divine. Ultimately, the danger of this teaching was that it denied that God sacrificed Himself for mankind. The Nestorians taught that the man Jesus died on the cross, but that the Christ did not die.
In fairness, Nestorius was struggling to understand how God could become man. He fell into grave error when he attempted to follow logically his premises. Among questions raised are these. If Jesus was not truly and fully God, if there were two distinct natures that were not combined in Him, then do we have an infinite sacrifice? Who died on the cross? Did a man die, in which case our sacrifice is finite and we have no covering for our sin—at best any covering is finite? Or did God provide Himself as a sacrifice for sinful man?