As a rabbinical student, I learned that should anyone generate a novel understanding of the text (hiddush, in Hebrew), two questions need be asked: first, is this novel understanding of the text correct? and second, why has no one thought of this before? These two questions apply in consideration of Exodus 14:18.
Confronted by the sea ahead of them and pursued by the Egyptian behind them, the Israelites are nearly in a panic. God offers Moses reassurance. The sea will split, the Israelites will pass through, and, in their stubborn confidence, the Egyptians will pursue them only to be drowned in the collapsing walls of water. Thus, the Egyptians “will know that I am the Lord.” Leaving aside the question of what use it would be for Pharaoh and the Egyptian to “know that God is the Lord” when they are drowning, there is a textual conundrum to consider. When Moses and Aaron first appear before Pharaoh demanding that he release the Israelites from bondage (Exodus 5:1), Pharaoh is puzzled. He wants to know in which God’s name they speak. The God to whom they refer is unknown to him. “I do not know the Lord,” he says (Exodus 5:2). And so, he is resistant to comply.
As matters worsen for the Israelites, God raises Moses’ spirits by saying that even though Pharaoh will be stubborn and unsympathetic, ultimately, he will yield: “the Egyptians shall know I am the Lord when I stretch My hand over Egypt” (Exodus 7:5), referring to the plagues mentioned in the previous verse. Hence, Pharaoh and Egypt will “know the Lord” as a result of the plagues. That being the case, why does God say that Pharaoh and the Egyptians will “know God” at the sea when, presumably, that knowledge was acquired previously?
Given the fact that no classical commentator I have perused addresses this question, any solution would be a novel one. And the solution I propose is that the text recognizes that some people are hard to convince. Even though they endured the plagues, Pharaoh and the Egyptians still have not come to “know God.” To be sure, Pharaoh released the Israelites but that was on account of the pressure of his courtesans and the weariness of affliction – not because of knowledge of God. He needed further proof. And that proof comes at the sea. According to the Midrash, Pharaoh survives and does come to that knowledge, but only after one further encounter.
The realization that some people are hard to convince is a modern idea emerging from a more sophisticated understanding of human psychology and would not be expected of earlier generations of commentators.