Raymond Brown makes this comment in his discussion of the sign at the wedding feast: “Scholarly interpretations to the contrary, John does not put primary emphasis on the replacing of the water for Jewish purifications, nor on the action of changing water to wine . . . nor even on the resultant wine. John does not put primary emphasis on Mary or her intercession, nor on why she pursued her request, nor on the reaction of the headwaiter or of the groom. The primary focus is, as in all Johannine stories, on Jesus as the one sent by the Father to bring salvation to the world. What shines through is his glory, and the only reaction that is emphasized is the belief of the disciples” (John I-XII, 103-4).
Point taken. Jesus is the focus.
But John has already made clear that Jesus can only be understood by His difference from Moses: The law came through Moses, but grace and truth through Jesus Christ. No man – including Moses – has seen God, but the only begotten God who is in the bosom of the Father has explained Him.
Without the Mosaic background, Jesus is a cipher, as the two disciples on the road to Emmaeus learned: Unless we know Jesus as the one spoken of by Moses and all the prophets, we cannot recognize Him. Our eyes are still closed.
So, even if we insist that Jesus is the focus of the wedding of Cana story, we must equally insist that the Jesus who is the focus is the Jesus-who-transforms-water-of-purification, Jesus-who-makes wine. That is the only Jesus we can know. It is the only Jesus there is.