Charles Ellicott Commentary John 6:15

"Jesus therefore perceiving that they were about to come and take him by force, to make him king, withdrew again into the mountain himself alone." — John 6:15 (ASV)

When Jesus therefore perceived... John has told us of the effect of the sign on the multitude. He also knows the reason for Christ’s retirement, while Matthew and Mark only state the fact that He retired to pray. They did not know that He wished to avoid that throng of people who thought of the Messiah as an earthly king, and would have carried Him with them to the great feast at the royal city. Luke does not contain this section, but compare the question recorded by him in John 9:18 and following, which grows immediately out of it.

A mountain. Better, the mountain, or the hill-country (John 6:3). He withdrew again to the place where He was before.