Mark 6:48c: He meant to pass by them...

Grudem in the study notes for the ESV Study Bible comments on that strange phrase in Mark 6, "He meant to pass by them."

Mark 6:48 The fourth watch is the time between 3:00 a.m. and 6:00 a.m. The Sea of Galilee is 696 feet (212 m) below sea level, resulting in violent downdrafts and sudden windstorms (cf. 4:37). Jesus sees their need and walks on water toward them (see Job 9:8; Ps. 77:20; Isa. 43:16). He meant to pass by them, not so that they would fail to see him (in which case he would have stayed farther away from them), but so that they would see him “pass by” (Gk. parerchomai), walking on the water, thus giving visible evidence of his deity (and thus answering the question they asked after he stilled the sea in Mark 4:41: “Who then is this … ?”). The passage echoes the incident where God “passed” before Moses (the same verb, parerchomai, occurs in the Septuagint of Ex. 33:19, 22; 34:6), giving a glimpse of his glory. But it also echoes Job 9, where Job says that it is God who “trampled the waves of the sea” (Job 9:8; the Septuagint has peripatōn … epi thalassēs, “walking on the sea,” using the same words as Mark 6:48, peripatōn epi tēs thalassēs) and then also says, “he passes by me” (Job 9:11, Gk. parerchomai). There is an implicit claim to divinity in Jesus’ actions.

Mark seems to use the same phrasing in Mark 6 as the Septuagint does for several passages identifying God in the Old Testament. God is pleased to give us short glimpses of his glory as He passes by. He does this to encourage us in our struggles as He did for the disciples as they struggled against the waves.