In the subsequent pesukim the Torah relates: “Moshe told his father-in-law about all that Hashem had done to Pharaoh and to the Egyptians on account of Israel, and about all the hardships that had befallen them on the way, and that Hashem saved them. Yisro was happy about all the good that Hashem had done for Israel, that He had rescued them from the hands of the Egyptians. Thereupon, Yisro said, ‘Blessed is Hashem, Who has rescued you from the hands of the Egyptians and from the hand of Pharaoh, Who has rescued the people from beneath the hand of the Egyptians. Now I know that Hashem is greater than all the deities, for with the thing that they plotted, He came upon them’” (Shemos 18:8-11).
The Mechilta elaborates on the conversation Moshe and Yisro had with each other. Moshe intentionally spoke to Yisro about all the events that happened leading up to that point in order to pull him in and bring him closer to Torah. Rebbi Yehoshua says Yisro was ‘stirred and happy over the benefits of the manna that one can taste bread, meat, fish, locust, anything he wants to taste in the world can be tasted from the manna which Hashem gave them.’ Rebbi Elazar Hamodai said Yisro was ‘impressed with the benefits of the “Well of Miriam” (the water which flowed from the rock) for the water which Hashem gave them can taste like old wine, new wine, milk, honey or any sweetness in the world.’ Rebbe Eliezer said Yisro was ‘impressed with the benefits of the Land of Israel for he was told that in the future there will be six good things: The Land of Israel, The World to Come, the Kingship of the House of David, a new world, the Priesthood and the Levites.’
Yisro was the first person at the time to praise Hashem with a language of blessing: “Blessed is Hashem…” The Mechilta, in fact, admits that this posuk is demeaning the Jews; for out of 600,000+ Jewish people not one of them got up and blessed Hashem until Yisro came around!
The Mechilta goes on to describe Yisro’s enlightenment. Until that point he had not admitted to anything. Even though, as the Vilna Gaon points out, Yisro recognized Hashem previously but now even more. Yisro said that as Hashem’s Name grew in the world people said that initially no slave was able to escape Egypt for it was completely closed, yet now over 600,000 people left Egypt. That is why “Hashem is greater than all the deities;” all the things the Egyptians wanted to use to annihilate the Jews, Hashem used against the Egyptians. The Malbim points out that Yisro recognized how Hashem exacted punishment, measure for measure, on the Egyptians; which only One who is in control of all powers is able to do.
Yisro was known to have tried every type of idol worship in the world. In fact, in the very next verse the Torah says: “Yisro, the father-in-law of Moshe, offered a burnt offering and sacrifices to Hashem.” The Malbim says this sacrifice was offered because he had converted to Judaism, but the Mechilta adds that the Torah was showing it’s astonishment, in a good way, that a person who was so involved in worshipping idols, giving libations to them and bowing down to them, could now bring offerings to Hashem. What awesomeness! (Click here for Hebrew text.)
Yet what convinced Yisro to embrace the truth? Yisro heard in detail from the greatest eyewitness, his son-in-law Moshe, of all the miracles that happened in Egypt and afterwards in the desert. But the Mechilta does not say that Yisro got inspired by the wonders of the plagues, the fact that all liquid turned to blood only for the Egyptians, even sap, juice, and their own saliva, or that hail fell down and cracked into fire, or that the darkness was so thick that the Egyptians could not move for three days. The Mechilta doesn't even mention all the miracles of the splitting of the sea into twelve parts, the Jews walking on dry land made out of marble with fruit trees to eat from, fresh water streaming out of the salty sea walls, etc. He doesn’t reference the incredible feat of food falling from heaven every day, a rock bringing forth water, and clouds by day and fire by night taking care of and leading the Jewish People through the desert.
So what made Yisro’s heart stir? It was the fact that an entire nation of slaves escaped Egypt which no other slave, not even one, was able to do before; and the fact that Hashem punished the Egyptions with such exactitude that is was directly measure for measure for what the Egyptians inflicted on the Jews. Yisro also was impressed that the food and water they were receiving in the desert tasted like anything in the world, as well as the benefits of the place they were going to and the living conditions they will eventually be living in.
What made Yisro convert was not the glitz and glamour. That might have been what got him in the door and brought him to Moshe to begin with; but he ultimately developed an intellectual appreciation for how Hashem handled things which caused him to embrace the truth.