Summary: The underlying reason for all of Jesus' mighty works is clearly stated in John 2:11, “In order that they might see, and seeing believe.”
Out of the vast amount of material available to John, the writer of the Gospel, he has carefully chosen his material as an eyewitness of all Jesus did and said,
In his writing he has a clear, guiding purpose. John 20:30-31 tells us, "Many other signs therefore Jesus also performed in the presence of the disciples, which are not written in this book; but these have been written that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name." So John has deliberately, chosen these particular miracles for the purpose that we might believe and the result of that belief will be life everlasting.
Ray Summers in his book, "Behold the Lamb," states that John selected these miracles because they make the greatest demand on faith. They go beyond the norm. In the synoptic gospels, Jesus restores sight to one who has lost it.
In John's gospel, He gives sight to one who was born blind. In the other gospels, Jesus brings back to life one who has been dead a few moments or hours.
In John's gospel, he brings Lazarus back from the dead after four days. John selected these miracles for the purpose of stimulating belief that the One who did these signs was indeed the Christ, the Son of God, and that by that faith they might have the eternal life which Jesus offered. Jesus' miracles, then, were manifestations of His glory as the Redeemer whom the Father had sent.
The wedding took place not far from Nazareth in the small village where Nathanael lived, Cana of Galilee. Notice the specifics. It must have been something of a family affair. The mother of Jesus, whose name is not given, but who is very specifically identified, seems to be at the center of arranging things. And Jesus and His disciples were invited. This is the first time Jesus is identified in an intimate way with His disciples, and they would surely not have been invited as a group had they been total strangers.
A wedding in those days was a great celebration, no little twenty-minute event.
The ceremony usually took place late in the evening ... on a Wednesday if the girl was a virgin and on a Thursday if she was a widow ... and would be conducted after a feast. Then there was a procession to the home of the groom, a joyous, noisy parade, with an open house and entertainment that went on for at least a week.
Surely the rich, deep meaning of marriage in Jewish religious life was in John's mind as he shared the account of this simple, shining even in Cana. That intimate relation between God and Israel is portrayed over and over again through the image of the marriage covenant. The fullness of the age of the Messiah was prophesied in Isaiah and spoken of so beautifully through the symbol of marriage, and the vision of the consummation of all history will be celebrated in the marriage of the "Lamb and His bride" when glory is given the Lord God Omnipotent (Rev. 19:7). How highly suggestive then that Jesus' first miracle, inaugurating the messianic age, should be the sign given at a wedding.