John Calvin on John 6:20-21

20. It is I: be not terrified We learn from them that it is in Christ’s presence alone that we have abundant grounds of confidence, so as to be calm and at ease. But this belongs exclusively to the disciples of Christ; for we shall afterwards see that wicked men were struck down by the same words, It is I, (John 18:6.) The reason of the distinction is, that he is sent as a Judge to the reprobate and unbelievers for their destruction; and, therefore, they cannot bear his presence without being immediately overwhelmed. But believers, who know that he is given to them to make propitiation, as soon as they hear his name, which is a sure pledge to them both of the love of God and of their salvation, take courage as if they had been raised from death to life, calmly look at the clear sky, dwell quietly on earth, and, victorious over every calamity, take him for their shield against all dangers. Nor does he only comfort and encourage them by his word, but actually removes also the cause of the terror by allaying the tempest.

John 6:22-25

22. Next day, the multitude standing on the other side of the sea, when they saw that there was no other ship there but only that into which his disciples had entered, and that Jesus had not entered into the ship with his disciples, but that his disciples had gone away alone; 23. And other ships came from Tiberias, near the place where they had eaten bread, after that the Lord had given thanks. 24. When therefore the multitude saw that Jesus was not there, nor his disciples, they also entered into the ships, and came to Capernaum, seeking Jesus. 25. And having found him on the opposite side of the sea, they said to him, Rabbi, when camest thou hither?