A number of events happen in the area of Mount Sinai at the end of Parashat Beshalach and the beginning of Parashat Yitro.
In the first story, the people are in Rephidim and don’t have water:
“From the wilderness of Sin the whole Israelite community continued by stages as the LORD would command. They encamped at Rephidim, and there was no water for the people to drink.” (Shemot 17:1)
God then tells Moshe to strike the rock, and notes that He is at Horeb:.
“I will be standing there before you on the rock at Horeb. Strike the rock and water will issue from it, and the people will drink.” And Moses did so in the sight of the elders of Israel.” (Shemot 17:6)
Horeb is identified with Sinai in a number of places in the Torah.
The next episode is the war against Amalek. It doesn’t mention Sinai (or Horeb) by name, but it can be understood that it took place there. First of all, the location of the people hasn’t changed:
“Amalek came and fought with Israel at Rephidim.” (Shemot 17:8)
Moshe then says, “I will station myself on the top of the hill” (Shemot 17:9), which Ibn Ezra identifies with Mount Sinai.
Moving to the next parasha, we see that Yitro came to Moshe at Sinai:
“Jethro, Moses’ father-in-law, brought Moses’ sons and wife to him in the wilderness, where he was encamped at the mountain of God.” (Shemot 18:5)
And most famously, the people stood to receive the Torah at Mt. Sinai:
“On the third new moon after the Israelites had gone forth from the land of Egypt, on that very day, they entered the wilderness of Sinai. Having journeyed from Rephidim, they entered the wilderness of Sinai and encamped in the wilderness. Israel encamped there in front of the mountain.” (Shemot 19:1-2)
This last passage caused difficulty for the commentators. It says that the Israelites had left Rephidim and arrived at Sinai. But why would this be mentioned now, after we just read three stories that took place at Sinai?
One solution – proposed by Rashbam on Shemot 18:13 and Ibn Ezra on Shemot 18:1, among many others- is that the Torah did not tell these stories in chronological order, and Yitro came to Moshe after the Torah was given. Others – like the Ramban on Shemot 18:1 – insist that the events happened in the order that the Torah presented them.
Each brings their own proofs. Ramban in general is opposed to changing the order of events in the Torah unless absolutely necessary. In addition, he says that had Yitro arrived after the giving of the Torah, they would have mentioned in their conversation, in Shemot 18:8-11.
Those who say the events aren’t in chronological order have a number of proofs. Some cite passages later in the Torah, like Yitro’s visit in Behaalotcha (Bamidbar 10:29-32) and Moshe’s retelling of the appointment of officers in the first chapter of Devarim, which don’t fit with the explanation of Yitro visiting (and leaving) before the Torah was given. Additionally, they note that in the story in Shemot, Moshe tells Yitro:
“When they have a dispute, it comes before me, and I decide between one person and another, and I make known the laws and teachings of God.” (Shemot 18:16)
The word for “teaching” there is Torah, and so it would only make sense that Moshe would say that after he had received the Torah.
So according to the approach that these events are not told in chronological order, how do they explain the reason for that change?
They provide two main reasons. One was to connect the story of Amalek with that of Yitro, to provide a contrast. Amalek reacted to Israel’s redemption from Egypt by attacking them, whereas Yitro reacted by praising God.
The second reason offered is to ensure the centrality of the giving of the Torah at Sinai. Of all the things that occurred there, Matan Torah was the most important, and so the Torah starts the narrative with the people arriving at Sinai, and then following that momentous event, continues directly into the many laws in Parashat Mishpatim.
One question then remains, which is unaddressed by those same commentators. Why then, does the parasha that includes Matan Torah not start with Shemot 19:1? Had the story of Yitro been the end of Parashat Beshalach, it would have aided both goals mentioned above: the connection between Amalek and Yitro would have been stronger, and the centrality of Matan Torah at Sinai would have been more evident.
I propose the reason that Parashat Yitro starts in chapter 18 instead of 19 was to teach an important lesson. Yitro’s story shows that Moshe, as important as he was, was not the only source of knowledge or authority. Yitro, an outsider, comes and gives him important advice. And that advice was to delegate authority to judges and officers among the people. Without that introduction, one might assume that Moshe was nearly omniscient or omnipotent. That’s a dangerous approach to take towards any leader, even Moshe, the greatest of prophets. So the Sages placed the story of Yitro before the story of Moshe receiving the Torah to ensure we retain that perspective.