When Bnei Yisrael heard the first two of the Aseres Hadibros from HKB”H they knew it was the real deal. The next step however, is to take that knowledge into action.
When we hear about an amazing story, or maybe even a miracle, there is so much more that meets the eye. Every detail adds to the greatness of what took place.
When the Jews fought with Amalek, their knowledge of Hashem didn’t suffice. They needed a visual representation of this, which helped them in their battle.
When they reached the Yam Suf, Moshe Rabbeinu and Bnei Yisrael had nowhere to turn. What he didn’t realize was that sometimes you just got to go on…your davening has already been answered.
The Egyptians were able to replicate the first two makos. However, their error was that they didn't understand that the way Hashem did the two makos was vastly different than how they did.