I have to admit, this is not a story I've given much thought to in the past. It's not simply that it's unbelievable,1 because there are other stories in the Gospels that are also unbelievable, but I have still found meaning in them. But this miracle story has always struck me as a little bit frivolous, like it's a silly party trick.
I've changed my mind about that, though, and the key is understanding the symbolism of the jars.
The stone jars, we're told, were "for the Jewish rites of purification" (v.6). They were made of stone because stone would not become ritually contaminated or impure. Normally a family would only have one such jar, but here there are six.
Some scholars claim that the reason for this is to give Jesus a large quantity of water to work with. "This exaggeration," says one, "owes to the narrator’s desire to represent a miracle of transformation of super proportions in this story."2 Another says, "the great quantity they contained," was meant to reflect "the fullness of Christ’s grace."3 Perhaps.
Some scholars, on the other hand, have suggested that the number six is meant to be understood symbolically. Andrew Lincoln, for example, writes, "The number six may well...represent the imperfection of insufficiency of the old order of Judaism."4 The transformation of the water into wine represents the coming of the new order represented by Jesus:
In the Jewish Scriptures wine in abundance signifies the salvation of the end time—'The time is surely coming, says the Lord, when...the mountains shall drip sweet wine, and all the hills shall flow with it. I will restore the fortunes of my people Israel,...they shall plant vineyards and drink their wine' (Amos 9:13–14; cf. also Isa. 25:6; Jer. 31:12; Joel 3:18)...In addition, wine stands for life and joy (cf. Ps. 104:15; Eccl. 10:19; Sir. 31:27–8; 40:20). In inaugurating the new order, Jesus provides life that is to be enjoyed.5Such a reading inevitably brings up the problem of anti-Judaism in the Fourth Gospel, which is obviously a matter of concern. But I would suggest that this text can be understood as conveying something that is actually faithful to the transformation that Jesus sought to bring about through his ministry.
This Gospel's frequent portrayal of "the Jews" as Jesus's opponents is obviously problematic, and not something Jesus himself would have recognized. But we shouldn't forget that, during his actual lifetime, Jesus was often in conflict with some of his fellow Jews, specifically about their way of being Jewish.
Often the point of contention was the purity code of the Torah. Jesus had little time for the purity code, particularly when following it meant victimizing others. The concern for purity, for recognizing distinctions between "clean" and "unclean," belongs to a relatively immature (but very common) stage of religious development. It creates binary oppositions between classes of people, generally favouring one side to the detriment of the other.
Jesus sought to overcome this by promoting an ethic that valued compassion over purity, but the defenders of the purity system—people who benefitted from being in the favoured side of each binary—predictably resisted. His opponents were mostly Jewish, yes—but the kind of thinking he opposed was (and is) found in every religion, including our own.
The transformation of water into wine represents the transformation we are undergoing, and have always been undergoing: the growth beyond the divisive ways of thinking that denigrate large segments of humanity in support of one favoured class, people who resist the new order represented by Jesus, and the belief that "life...is to be enjoyed."
 That this is not an historical event would be affirmed by "virtually all mainstream scholars," according to Marcus J. Borg (Jesus: Uncovering the Life, Teachings, and Relevance of a Religious Revolutionary, 57). While many scholars would dismiss it out of hand simply for being a "miracle," there are plenty of reasons someone who is open to the possibility of miracles might nevertheless arrive at the same judgment. The most extensive argument I've yet come across is from John P. Meier, A Marginal Jew, 2.934-950.
 Ernst Haenchen, John (Hermeneia), 1.173.
 George R. Beasley-Murray, John (WBC), 35.
 Lincoln, The Gospel According to Saint John (BNTC), 129. Raymond Brown dismissed the attempt to find symbolism in the number six as "farfetched" (The Gospel According to John [AYB], 1.100), but he didn't elaborate.
 Lincoln, 129.