What Jesus did here in Cana of Galilee was the first of the signs through which he revealed his glory; and his disciples believed in him. (John 2:11 NIV)
Jesus performed many miracles during his earthly ministry (John 20:30), but John only records seven of them. And he does so for a very specific purpose, which he shares here. The term John uses for miracles is instructive, calling them ‘signs’. A sign gives direction, pointing us toward something. And that is how John understood Jesus’ miracles. They were a sign to reveal to us the glory of Jesus (John 1:14) so that we might believe and, in believing, have life (John 20:31).
We might question why Jesus would turn water into wine, especially since the wedding guests already had a lot to drink. But that misses the point of what John is recounting here. In this miracle, Jesus revealed his glory, and that changed how his disciples related to him. No longer was he just a teacher. Now he was revealed as a miracle worker, as someone having power with God, and his disciples put their faith in him. Whenever we see the miraculous, it should direct our attention toward God and lead us to glorify him. True signs, or miracles, always reveal God to us and glorify him.