Jesus went up into the mountain, and he sat there with his disciples.

 We must remember two facts. At the north end the lake was no more than four miles across; and John tens us that the disciples had rowed between three and four miles; that is to say, they were very nearly at their journey's end. It is natural to suppose that in the wind they hugged the shore of the lake, seeking what shelter they might find. That is the first fact and now we come to the second. They saw Jesus, as the King James Version and Revised Standard Version have it, walking on the sea. The Greek is epi ( G1909) tes ( G3588) thalasses ( G2281) which is precisely the phrase used in John 21:1, where it means--it has never been questioned--that Jesus was walking on the seashore. That is what the phrase means in our passage, too. 