“Jethro priest of Midian, Moses’ father-in-law, heard all that God had done for Moses and for Israel His people” (Exodus 18:1).
In his commentary, Rashi quotes the words of the Midrash: “What was the particular report which he heard that made him decide to come? — The parting of the Red Sea and the war with Amalek” (cf. (Mekhilta d'Rabbi Yishmael 18:1:1; Zevachim 116a). In other words, there were two reasons that led Jethro to convert to Judaism: first the parting of the Red Sea, but this alone was insufficient reason without the victory of Am Israel over Amalek.
These things are somewhat puzzling. From Rashi's words, we see that when Jethro heard about the parting of the Red Sea, he still did not move to come to Moses in the desert. Only after hearing about the Amalekite war as well, did he finally awaken, leave his land and meet up with his great son-in-law and the people of Israel.
This is difficult to understand, since ostensibly in the Amalekite war, Israel’s victory can be accepted as a natural thing and not a miracle, because that is the way of the world in wars between nations, that sometimes one side wins and sometimes the other wins.
However, the parting of the Red Sea was a clear divine miracle, involving a complete change of the laws of nature, as described in the Torah: "the waters forming a wall for them on their right and on their left," (Exodus 14:22) and all the other accompanying miracles that took place there, both in the salvation of the people of Israel and in the drowning of the Egyptians.
All this was not enough for Jethro, who was a truth-seeker, researching and studying every kind of paganism in the world, and only after learning about the war of Amalek did he abandon his rich past in idolatry, and join the community of the servants of Hashem.
"The Great Eagle" Maimonides, in his book Mishneh Torah at the beginning of the laws of foreign worship, explains how the Generation of Enosh fell into idol worship.
They saw that G-d created in his world stars and the signs of the zodiac, and from this they understood that a man of flesh and blood has no right to worship Hashem and cling to Him. Rather, it is the stars and zodiac signs that are created as divine servants and to be mediators between human beings and Him. Therefore, by their understanding, they should worship these mediators, and not G-d.
In their distorted opinion, someone born is not able to work directly with G-d, and cling to Him.
This is what made them worship idols.
The sheer faith of Israel is: "they had faith in the Lord and His servant Moses." (Exodus:14:31). As regards Bnei Israel, when Moshe Rabbeinu came to them for the first time and showed them signs as proof he was sent by G-d, it was said of them: "And the people believed," and so their faith in G-d alone was renewed.
Only after the parting of the Red Sea, when Bnei Israel saw with their own eyes the faith of Moshe Rabbeinu in G-d alone, when they saw with their own eyes that everything would be settled by Moses: “lift up your rod… over the sea and split it” (Exodus 14:16), they saw that G-d gave control - control of his world - to someone born of flesh and blood like them, to Moshe Rabbeinu.
Then their faith in G-d was also completed, as it is said: "they had faith in the Lord and His servant Moses."
Then they came to know that between G-d and His creatures there is a direct connection without intermediaries such as heavenly bodies. Thus they came to know of the ability of flesh and blood to rise up and up, and as it ascends, it draws closer to the Creator of the world.
This is why one of the thirteen principles of faith is, to “believe with perfect faith that the prophecy of Moshe Rabbeinu, peace be upon him, is true, and that he was the father of the prophets, and that all the words of the prophets are true.”
That is to say, there was not only one person in the world who prophesied, Moshe Rabbeinu. Rather, he was just the father, and many prophets, the sons, followed him. A degree of prophecy can be the property of the people, as Rabbi Moshe Chaim Luzzatto (1707 Padua, Italy - 1746 Acre, Israel) explained in detail in his famous book “Path of the Upright”, the eleven levels in G-d worship that lead to prophecy.
In the Talmud, in Tractate Shabbat 89a, it is said that after the giving of the Torah, Satan came before G-d and asked him where the Torah was, and G-d told him that he gave it to the earth. Satan searched and did not find it, and returned to G-d and asked again where it was, G-d told him "I gave it to Moses,” so Satan went to Moshe Rabbeinu and asked him: "the Torah that G-d gave you, where is it?" Moses answered Satan with humility: “And what am I that the Holy One, Blessed be He, would have given me the Torah?" G-d said to Moses: “Since you belittled yourself, the Torah will be called by your name, as it is said: “Remember the Torah of Moses My servant””.
It follows, that was the purpose of G-d in saying this to Moses, if Moses wouldn’t accept that he was getting the Torah as someone of flesh and blood. Israel and the nations of the world would be wrong to think that someone born is not able to reach such a high spiritual level, the error of the Generation of Enosh. This is why G-d specifically named the Torah for Moshe Rabbeinu, to emphasize that all flesh and blood can ascend to a higher degree of holiness. Similarly, Maimonides wrote that every Jew can reach the level of Moses.
Bnei Israel, who were present at the parting of the Dead Sea, saw the involvement of Moshe Rabbeinu in the fulfillment of G-d’s will, and were able to have complete belief: "they had faith in the Lord and His servant Moses." Jethro did hear about the parting of the Red Sea, which was a change in the nature of Creation, a visible miracle that leads to the revelation of the Shechinah. And by virtue of this, he decided to worship Hashem, but this miracle still did not convince him to join the people of Israel. The parting of the Red Sea itself did strengthen him in his faith in G-d, but he had not yet reached the level of "they had faith in the Lord and His servant Moses." He could still worship Hashem from where he was without coming to join the people of Israel.
But in the war of Amalek, it is said: "whenever Moses held up his hand, Israel prevailed; but whenever he let down his hand, Amalek prevailed." (Exodus 17:11). And Chazal said in Mishnah Rosh Hashanah 3:8: "Did the hands of Moses make war when he raised them or break war when he lowered them? Rather, the verse comes to tell you that as long as the Jewish people turned their eyes upward and subjected their hearts to their Father in Heaven, they prevailed, but if not, they fell".
Which leads to a question: if Israel looks upward and subjects their hearts to their Father in Heaven when Moses raises his hands, why when Moses lowers his hands do they supposedly stop enslaving themselves to the Creator of the world?
It is precisely here that Jethro saw the absolute faith of the people of Israel in Moshe Rabbeinu as the generational leader - "they had faith in the Lord and His servant Moses." This is the power of faith of Am Israel in the Gadol HaDor Moshe Rabbeinu, and only according to the guidance of the Gadol HaDor will the people of Israel do G-d’s deeds, and without clear guidance from the Gadol, they do nothing.
Only here did Jethro realize that the uniqueness of the people of Israel is in its devotion to its leaders Gedolei Yisrael, and that he will be able to reach this level only if he joins Am Israel, and in this way attain his desired spiritual completion.