Albert Barnes Commentary Isaiah 51:15

"For I am Jehovah thy God, who stirreth up the sea, so that the waves thereof roar: Jehovah of hosts is his name." — Isaiah 51:15 (ASV)

But I am the Lord your God - In order to show them that he was able to save them, God again refers to the fact that he had divided the sea, and delivered their fathers from bondage and oppression.

That divided the sea - The Red Sea. The Chaldee renders this, ‘That rebuked the sea.’ The Septuagint, Ὁ ταράσσων ho tarassōn – ‘Who disturbs the sea,’ or, ‘who excites a tempest.’ Lowth renders it, ‘Who stills at once the sea.’

The Hebrew word is the same which occurs in Isaiah 51:4, where it is rendered, ‘I will make my judgment to rest’ (רגע râga‛). Probably the idea here is that he restrains the raging of the sea as if by fear; that is, makes it tranquil or still by rebuking it.

He had this power over all raging seas, and he had shown it in a special manner by his rebuking the Red Sea and making it rest, and causing a way to be made through it, when the children of Israel came out of Egypt.

The Lord of hosts is his name - (See the notes at Isaiah 1:9; compare the notes at Isaiah 42:8).