In Parshas Yitro, when Yitro arrives to meet Moshe he repeatedly exclaims in wonder over G-d's goodness in redeeming the Jews, but it is something else that causes him to state, that he now knows that G-d is greater than all deities. What is that thing? It is the Egyptians drowning as they had drowned the Jewish children.
What is the significance of that? Is Yitro a vengeful person? Does he believe in G-d because he sees Him as a vengeful force?
Let's explore what happens next in this Parsha. Yitro proposes a full blown justice system. It's clear that Yitro is a person interested in justice. What he recognizes about G-d's actions is that they involved not merely the outpouring of wrath, for wrath is only a function of force. Force is power, but it alone is not something for a truly intelligent and moral person to worship. He recognizes the redemption of the Jews, but that alone does not convince him either, for mercy too is a function of power. Those who have power can show mercy. But not all mercy is proper or correct and like wrath, must be used properly.
Yitro's recognition of G-d's greatness came from seeing that balance of mercy and power, it came from seeing that G-d punished the wicked according to their deeds. This is justice and it was justice that Yitro valued. When we first read about him, he is reproving his daughters for failing to invite in the man who rescued them. And while we do not know for certain exactly what caused this downfall in his status at home, it was likely a pursuit of justice.
Sandwiched between the attack of Amalek and the giving of the Torah at Har Sinai, Yitro's arrival seems off-topic, a bit of personal trivia thrust among great events. Even his advice to Moshe seems a minor matter, but it isn't at all.
When Amalek attacks, he attacks those who had fallen behind. In an equitable society, no one falls behind. The commandments that are given at Har Sinai, many of them are concerned with systems of justice enacted against murder, theft and enslavement... among others. For that society to exist, Yitro was needed to bring his concern for justice in the enactment of a system of justice.
While Moshe's ability to lead the Jewish people would always be superior because of his divine link, the Jewish people as a society would not always be able to count on prophets or count on those in power being divinely inspired. They would not a reliable system of justice transcending the tribal systems of leadership, one that rose above elders and aimed for a higher standard of fairness. Only then would they be prepared to receive commandments that required justice to punish the wicked and free the innocent.
Having been transformed by the revelation of G-d's justice at the sea, Yitro wanted to bring that same standard of justice to the Jewish people.