The disciples are struggling against the wind at night when Jesus approaches across the water. Their fear shows that what they see lies outside ordinary human experience.
Mark adds the puzzling statement that Jesus intended to 'pass by' them, language that becomes meaningful against Israel's Scriptures.
Job 9:8 describes God as treading upon the waves of the sea, and Job 9:11 speaks of God passing by unseen. Exodus 33-34 and 1 Kings 19 also use 'passing by' language in theophanic revelations to Moses and Elijah.
The convergence of sea-walking and passing-by language makes a divine self-manifestation reading especially compelling, although the Exodus allusion is debated more than the Job connection.
Jesus approaches by walking on the sea. When the disciples cry out in fear, he tells them to take courage and identifies himself: 'It is I; do not be afraid.' He enters the boat and the wind ceases.
Mark then stresses their failure to understand, connecting their amazement with their incomprehension concerning the loaves.
The strongest case does not depend on treating the Greek ego eimi automatically as the divine name. It rests on the complete scriptural pattern: Jesus walks where Job says God walks, 'passes by' in language associated with divine manifestation, and exercises mastery over the sea.
This is one of Mark's strongest narrative presentations of Jesus within the identity and actions of Israel's God.
The disciples are terrified and then utterly astonished; Mark says they did not understand and their hearts were hardened.