The Mekhilta offers an alternate reading of "You have guided them in Your strength." Here, "strength" does not refer to the Torah. It refers to the kingdom of the house of David. God guided Israel through the sea in the merit of the Davidic monarchy they would one day establish in the land.
The proof text is characteristically elegant. The Psalmist writes (Psalms 21:2): "O Lord, in Your strength the king will rejoice." And Hannah's prayer in (1 Samuel 2:10) declares: "And He will give strength to His king." In both verses, "strength" and "king" are bound together. The word "strength" in the Song at the Sea therefore points to royalty — specifically, to the dynasty of David.
This interpretation creates a breathtaking timeline. The Israelites crossing the Red Sea around 1250 BCE were being guided by the merit of a kingdom that would not be established until David took the throne in Jerusalem centuries later. The splitting of the sea was not just a response to Egyptian oppression. It was an act shaped by the entire sweep of Israelite destiny, including a future king who had not yet been born.
Where the first reading saw Torah as the guiding merit, this variant sees monarchy. Both agree on the essential principle: God acts in the present on the strength of what Israel will become.