And it can be explained, based on what we have discussed elsewhere, that the first days of Pesach, which are in remembrance of the Exodus from Egypt, their service is faith (אמונה), and the last days, which were before the Splitting of the Red Sea, their service is trust (בטחון). Therefore, they were commanded not to pray, but to journey into the sea with complete trust and peace of mind, certain that they would be saved and that no harm would befall them at all.