The nun told you that in reference to the wedding at Cana, a story found in only in John's Gospel. Jesus was not ready to begin his public ministry yet. His reply to Mary when she told Him "They have no more wine" was "Woman, my HOUR has not yet come." But she trusted Him so completely, she told the servants, "Do whatever He tells you." And Jesus did her bidding, hastening the HOUR that figures so largely in John's Gospel, the HOUR of the crucifixion and redemption of the world. Pretty big deal there. Jesus doesn't HAVE to do anything; but these things were recorded that we might believe, as St. John says.