Exodus 15:19

(19) This verse is parenthetic. It forms no part of the “Song of Moses.” Originally, perhaps, when that song was a separate document, it was appended as an historical comment, showing the occasion on which the poem was composed. When the records of Moses were collected—either by himself, towards the close of his life, or by Joshua—the addition was kept, although it had become unnecessary for the original purpose. As it stands, it emphasises the great fact of Israel’s final deliverance—the nucleus around which Exodus gathers itself.