John Gill Commentary Matthew 8:1

"And when he was come down from the mountain, great multitudes followed him." — Matthew 8:1 (ASV)

When he was come down from the mountain
Into which he went up, and preached the sermon recorded in the "three" preceding chapters:

great multitudes followed him :
which is mentioned, partly to show, that the people which came from several parts, still continued with him, being affected with his discourses and miracles; and partly on account of the following miracle, of healing the leper, which was not done in a corner, but before great multitudes, who were witnesses of it:

though some think this miracle was wrought more privately.