Albert Barnes Commentary Exodus 15:19

"For the horses of Pharaoh went in with his chariots and with his horsemen into the sea, and Jehovah brought back the waters of the sea upon them; but the children of Israel walked on dry land in the midst of the sea." — Exodus 15:19 (ASV)

For the horse ... - This verse does not belong to the hymn, but marks the transition from it to the narrative.