There is a first time for most things such as the first job and the first meeting or the first sentence. Jesus worked the first miracle at his mother's request at the wedding of Cana. The first miracle was the third manifestation of his divinity. The first manifestation was at his birth in Bethlehem and the second one was at his baptism at the river Jordan. Both of these were revealed by God the Father. The third manifestation was done by Jesus himself and it was at the wedding in Cana.
At his mother's request Jesus changed the water used for purification into the finest wine. In doing this Jesus revealed his heavenly power and his earthly mission to his disciples. His mission was to renew everything in himself. This renewal is an extraordinary act of God's love and mercy for the human race. Jesus renewed all things in himself not through words- not simply by preaching. His preaching was accompanied by His submission to the very cruel actions of his own people. He paid a costly price, sacrificing his own sacred life and pouring out His most precious blood through His Passion. On the cross he revealed his greatest desire, calling on the Father to forgive our wrong doings. The replacement of purification water with the wine at the wedding and the blood on the cross open for us the meaning of the new baptism Christ offers.
Wedding and banquet imagery is used to symbolize the new heaven and new earth. The miracle changing the water into the finest wine indicates that in Christ everything is at its best and most magnificent. The chief steward, the official of the wedding commented to the bridegroom that people often serve the good wine first and keep the cheaper one till later on but you do something out of the ordinary. The bible gives us a different meaning. It tells us Jesus worked the miracle to
'Let his glory be seen and his disciples believed in him'. v.11
The disciples knew Jesus' power after the miracle, but Mary knew prior to it. She firmly believed in Jesus and told the servants to carry out Jesus' instructions. His mother and the servants and his disciples knew where the 'best' wine came from and they were aware of about his mysterious power and glory. Apart from them, the rest of the wedding guests, including the chief steward, knew nothing about Jesus' mysterious power and glory. Precisely when the miracle occurs remains a mystery but that isn't the point; the most important point is the divine power behind the miracle because without it there was no miracle at all. Jesus concealed his identity from the public simply because 'his hour has not yet come'. The disciples already believed in Jesus and had became his inner circle. The miracle confirmed and reinforced their faith and that was the proper response to the miracle.
The "hour" in this context is used to refer to Jesus' glorification through his death and resurrection. Jesus used the wedding feast to talk about God's kingdom and to this end the true bridegroom is none other than Jesus himself in the 'heavenly banquet' and we are invited to take part in the preparation for coming of the heavenly banquet.