The first Pasuk of Parshat Yitro states that “Vayishma Yitro,” Yitro heard of all the miracles Hashem performed for the Jews, including the splitting of the sea, the Makot in Egypt, and the victory against Amalek. The juxtaposition of Yitro’s arrival at the beginning of this week’s Parsha and the attack of Amalek at the end of last week’s Parsha shows the differences between good and evil in the world. Both Yitro and Amelek heard of the miracles in Egypt and splitting of the sea, but they responded in totally opposite ways. Yitro reacted by joining with the Jews and converting his family, while Amalek became the symbol of evil by defying Hashem and launching an unprovoked attack on a weary and weak Jewish nation. Miracles do not transform nations like Amalek who defy Hashem; no matter what Hashem does, how extraordinary a miracle He performs, Amalek will refuse to recognize the hand of Hashem and will interpret the events to suit its own purposes (see Ibn Ezra’s long commentary to Shemot 18:1).
The Or HaChaim states that Yitro converted his family and joined with the Jews only after both events occurred: the miracles in Egypt and the war with Amalek. The miracles in Egypt could have been interpreted as a punishment for Pharaoh’s and the Egyptians’ refusal to obey Hashem and recognize Him as the only God. However, the Makot did not prove that Hashem would be compassionate for the sake of the Jews. However, the win over Amelek proved that Hashem would intervene purely on behalf of the Jews, not just to punish the enemy for defying Hashem.