Sforno on Exodus 15:1/ספורנו על שמות ט״ו:א׳

1אז ישיר, he agreed to sing this song.

2כי גאה גאה, He alone is entitled to feel this sense of superiority seeing He is the source of all goodness in the universe. This is in contrast to Pharaoh who boasts about having created the Nile as the source of Egypt’s affluence, (Ezekiel 29.3) a totally spurious claim.

3סוס ורוכבו רמה בים, a reference to Pharaoh and his horse. Compare Psalms 136,15 ונער פרעה וחילו בים, “He tossed Pharaoh and his armed might into the Sea.”