What does John 2:7 mean?

Six stone jars (John 2:6) would have held between 120 and 150 gallons of water, or between 450 and 560 liters. That's not an incredible amount of water. But Jesus is acting in response to a married couple's need (John 2:3). He's in the process of transforming this into quite a bit of wine (John 2:8–10).

It's no accident that Jesus involves the servants in His miraculous work. Jesus frequently asks people to play some part in His miracles. The power is entirely His, but God wants us to express faith and obedience. In the Greek of John's gospel, the action-word for "faithfulness" is used nearly one hundred times, but the noun for "faith" isn't used at all. True faith in Christ is living, active, and in motion.

Also, the gospel is about changing us as people, not re-creating us from scratch. Rather than just conjuring wine into existence, Jesus asks servants to supply water, so that He can change it into wine. And, as He often does, He expects us to take advantage of everything He offers: the servants filled the jars "to the brim."