"And many other signs truly did Jesus in the presence of His disciples, which are not written in this book: 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" (John 20:30-31).
The Gospel of John was written explicitly to lead people to salvation through faith in Christ. To do that, they must be shown that He was the very Son of the omnipotent God. This in turn required that certain great events in His human life become part of the written Word, the Holy Scriptures.
John's Gospel was written after the Jewish dispersion in 70 A.D. and so was written especially with the pagan world of evolutionary humanism in mind. Both Jew and Greek needed to know that Jesus was more than a great man, for He was the very Creator Himself.
Therefore, John began his evangelistic appeal with a great affirmation of creation, starting with the very words of the only real record of ex nihilo creation in the ancient world - that is, the book of Genesis. "In the beginning was the Word, . . . the Word was God. . . . All things were made by Him. . . . He was in the world, and the world was made by Him, and the world knew Him not" (John 1:1,3,10).
Then John described in detail seven great miracles of Christ none of which could ever be duplicated by any sorcerer or magician. Solely by His own spoken word, He turned water into wine, healed a dying lad six miles away, gave perfect limbs to a life-long crippled man, created food for a multitude, walked on water, made perfect eyes for a man born blind, and restored a friend to life who had been dead four days. Finally, He arose from the dead Himself. Many have been those through the years who, on reading this wonderful gospel, have said with Thomas, "My Lord and my God!" (John 20:28). HMM