But he said to them, "I AM. Don't be afraid."
And he would have passed them by ...  (Mark 6:48) is another detail omitted by John, but it shows that Christ will always pass his disciples by unless they call upon him.  It was this same character of withholding a blessing until it was requested that appeared in Jesus' refusal of the plea of the Canaanitish woman  (Matthew 15:23), and when he "made as though he would go further" (Luke 24:48) while walking with the disciples on the road to Emmaus.