1)
What is the comparison "Molicham ba'Tehomos ka'Sus Midbar Lo Yikashelu"?
1.
Rashi: It does not stumble, for it is smooth land. So they did not stumble in the depths.
2.
Radak: Do not say that the sea floor was not so dry that they could go strongly in it or run in it. He brought them through like a horse that runs in the Midbar - a flat land without rocks or mud. It was so hard that they did not stumble in it. Malbim - this was one of 10 miracles in Keri'as Yam Suf (Avos 5:5). It was to add to the miracles and make it easier to go. Merely removing the water was enough to enable them to pass through.
