What do we learn from "Darachta va'Yam Susecha"?
Rashi: He trampled with his soldiers, which were heavy like sand of the sea.
Radak (8, 14-15): Your horses trampled in the sea, and You brought Your nation Yisrael through it, and cast Egypt in the depth and drowned them. "Susecha" refers to Pharaoh's horses - "Sus v'Rochevo Ramah va'Yam" (Shemos 15:1). Hashem removed their chariots' wheels, and they recognized that Hashem is fighting for Yisrael - "va'Yasar Es Ofan Markevosav... Anusah Mipnei Yisrael Ki Hashem Nilcham Lahem b'Egypt" (Shemos 14:25). I.e. just like Hashem fought for them in Egypt, so He fights for them now (at the sea). They saw Hashem split the sea for Yisrael, and took them through on the dry land, and Egypt could not pass - "va'Yaham Es Machaneh Egypt" (ibid. 24).
What is the meaning of "Chomer [Mayim Rabim]"?
Targum Yonasan: Bi'Dgor (a pile). Rashi - this is like "Chamarim Chamarim" (Shemos 8:10). Radak - the water piled up - "Nitzevu Kemo Ned Nozelim" (Shemos 15:8).
Malbim: You will split the sea, like earlier. Just the contrary - the waters will be noisy and rage. This is a metaphor for when the Mezid water will rise with Hashem's command and not be humbled due to fear of Him. Just the contrary - the water will storm to drown Yisrael in their clamor. This is also a metaphor for when the nations will gather for the war of Gog and Magog like mighty waters. They will not calm from their fury; they clamor to swallow and destroy Yisrael.
