See this passage explained in the notes at Matthew 14:22-36.
They considered not the miracle of the loaves - They did not remember or call to mind the "power" which Jesus had shown in feeding the five thousand by a miracle, and that, having done that, he had power also to save them from the storm.
Their heart was hardened - Their "mind" was dull to perceive it. This does not mean that they were "opposed" to Jesus, or that they had what we denominate "hardness of heart," but simply that they were slow to perceive his power. They did not quickly learn, as they ought to have done, that he had all power, and could therefore allay the storm. The word "heart" is frequently used in this sense. See Ephesians 1:18, in Greek; Romans 1:21; Romans 2:15; II Corinthians 4:6.
They knew him - They "recollected" Jesus, because he had been there before and worked miracles.
The border of his garment - Compare the notes at Matthew 9:20.
Other Barnes' Notes entries containing Mark 6:54:
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