The overriding principle reason for the gospel of John...the reason John wrote it...Joh 20:31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name. Yet in doing so, proving that Jesus was the only begotten Son of God, John completely ignored Bethlehem and the events of the incarnation, except for one oblique reference, "the Word became flesh". If John was going to prove Jesus was the Son of God because of the incarnation, then surely he would have mentioned Luke 1:35 , but no. The prime reason therefore for Christ being called the Son of God cannot be His birth at Bethlehem. There must be another reason.
The signs that John gave were signs of Christ‘s divinity. Under the inspiration of the Holy Spirit he was led of God to show that Christ was the divine Son of God. This can clearly be seen in his opening words:
In the beginning was the Word, and the Word was with God, and the Word was God. John 1:1
In order to fulfil the purpose in writing his Gospel (that Jesus was the Christ, the Son of God), the very first thing that the Holy Spirit led John to write was that Christ, in His pre-existence, ―was God. From the outset therefore, John was saying to his readers that there are two divine personages who are both rightly termed God (Gr. Theos). This was the opening thrust of his Gospel. John then proceeded to reinforce his opening words. He did this by saying that all things were made by the Word and without him was not any thing made that was made (John 1:3). Christ therefore, says John, is our Creator. This is the highest possible claim to divinity. Only divinity is not created.
These are amongst the opening thoughts that John sought to impress on the minds of those who would read his Gospel. First he shows that Christ is God (1:1). Secondly he shows that Christ was in the beginning with God (1:2). Thirdly he says that Christ is our Creator (1:3). These opening words are the very foundation for everything he would write.
Many events in the life of Jesus were exclusively mentioned by John, such as the resurrection of Lazarus, the changing of water into wine, and many others. Many talks were reported by John alone...the prayer of John 17, the talk with Nicodemus, and the woman at the well. All written to prove Jesus was the divine Son of God.
Throughout his Gospel, (and his letters), John repeatedly makes reference to Christ as being the Son of God. He also cites Jesus as continually speaking of God as His Father. This is the golden thread that runs through his Gospel from beginning to end. The terminology the Son of God therefore is the equivalent of saying that Christ is God. The question remains though: How could Christ, in His pre-existence, be God, yet at the same time be with God? (John 1:1). Is He the same God as He was with (the Father) or is He a different God? The answer is found in Christ‘s relationship to God – meaning in His Sonship.
For Christ to be the divine Son of God He must be begotten (brought forth) of God. If He is not begotten (brought forth) of God then He can neither be a true Son nor truly God. Everything depends upon His Sonship to God. If Christ is deprived of His true Sonship then He is deprived of His true Godship (Godhood). John wrote in the prologue to his Gospel
―And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth. John 1:14
―No man hath seen God at any time, the only begotten Son, which is in the bosom of the Father, he hath declared him.John 1:18
John later wrote (relating the conversation that Jesus had with Nicodemus)
―For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. John 3:16
―He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.‖ John 3:18
Amongst various scholars there is a consensus of opinion that the words found in the above two verses were not spoken by Jesus. This is because these scholars regard Christ‘s conversation with Nicodemus as ending at verse 15. Whilst I am not going to debate this issue here, it is true to say that whichever way this is viewed, it does not detract from the fact that the Holy Spirit inspired John to write these words. This means that even if they were only John‘s comments, they are as true as if Jesus Himself had spoken them. I may be wrong, but I think that Jesus did speak these words. John also wrote in one of his pastoral letters
―In this was manifested the love of God toward us, because that God sent his only begotten Son into the world, that we might live through him. 1 John 4:9
On two occasions with His own voice, God confirmed Christ‘s Sonship to Himself. The first was at the baptism of Jesus. The second was at His transfiguration
―And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased. Matthew 3:17
―While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him. Matthew 17:5From the above it can be seen that this Sonship was not because of Christ‘s human birth at Bethlehem but because of His pre-existent relationship with God. To put it another way: According to the Word of God, Christ had a pre-existent Sonship.