Why was Yisro sent home?

Question

After hearing about the miraculous things Hashem did for Bnei Yisrael when taking them out of Mitzrayim, Yisro (Moshe's father-in-law) travels from Midian and comes for a visit.

I would say it's almost universally accepted that Yisro ended up converting and joining Bnei Yisrael when he comes and talks to Moshe about what happened.

If he did convert, then why does Moshe send him back home to Midian (Shemos 18:27); shouldn't he have stuck around with Bnei Yisrael, especially since they were to receieve the Torah soon at Har Sinai?

^{(Of course, the Torah is not in chronological order so it would be easy to say that Yisro was sent back home after they received the Torah, and that the Torah only puts Yisro's visit and return here as a matter of reader convenience.)}

Why was Yisro sent back home instead of living in the desert with Bnei Yisrael and eventually entering the land, and more importantly why did Moshe do this? Because the passuk says "vayshallach Moshe es chosno" - Moshe sent his father-in-law away.

The Mechilta (as referenced by Rashi) writes that he went home to convet the other members of his family, but does this imply that he returned, along with his new converts, back to Sinai?

Answer 1

according to Yisro 18:27

Moses saw his father in law off, and he went away to his land.

Moshe Rabbeinu did not send him away but saw him off with honor when he (Yisro) decided to go back to Midian.

Rav Hirsch translates this as

And Moses let his father-in-law depart and he went his way to his own land.

Art Scroll says that according to Rashi and Seforno this actually happened the following year and is only mentioned in brief in order to conclude the narrative. This is like mentioning the death of Terach, Avraham, or Yitzchak at the end of their stories even though it actually happened many years later. The incident in Bamidbar is a lengthier retelling of the same incident.

After the year, Jethro returned home to convert his family to Judaism. He remained in Midian, but his children joined the Jewish people, who showed their gratitude by giving his family a fertile tract of land near Jericho. According to Ramban, however, Jethro actually left at this point to convert his family and then returned.

Other meforshim

ר"י קרא

וישלח משה את חתנוא – לשנה שניה לפי. שפתח בביאתו סיים בחזרתוב. (כ״י סנקט פטרבורג 118.1 בשם ר׳ יוסף)

In the second year, since it started with his arrival, it ends with his departure.

רד"צ הופמן

לפי דעתנו, שהארגון מחדש של מערכת-השפיטה ומערכת המינהל הונהג רק בסיני1, אפשר ששילוחו של יתרו זהה עם המסופר בבמדבר (י, כט-לב). אך השוה הערתנו למעלה ב, יח. לפי רמב״ן2חזר יתרו אל ישראל פעם נוספת, בשנה השניה ליציאת מצרים, ואז נענה בחיוב לבקשת משה להישאר עם ישראל, וכפי שגם משתמע מן הספרי3. והשוה גם דברי רמב״ן בתחילת פרקנו, שם הוא מדבר על ישיבת הקיני בין העמלקי. עם זאת יש לזכור, שיש דעה4, שאין חובב המוזכר בפרשת בהעלותך זהה עם יתרו חותן משה, אלא זה בנו של יתרו, כלומר גיסו של משה

From memory IIRC, there are those who say that Yisro could not be there for matan torah because he had not been part of the exodus. However, I do not have the citation for that possibility.

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Answer 2

To add to Sabbahillel's answers (mefarshim here):

Seforno (18:27) explains that Yisro went back because he was old, but that Yisro's children stayed:

וְזֶה אוּלַי מִצַּד זִקְנָתוֹ, כְּעִנְיַן בַּרְזִלַּי בְּאָמְרוֹ ״יָשָׁב נָא עַבְדְּךָ וְאָמֻת בְּעִירִי עִם קֶבֶר אָבִי וְאִמִּי״ (שמואל ב י״ט:ל״ח). אֲבָל בְּנֵי יִתְרוֹ הָלְכוּ עִם יִשְׂרָאֵל לָאָרֶץ בְּלִי סָפֵק

Netziv there explains similarly, that he left his family behind with Benei Yisrael, and went back to quickly sell his remaining possessions.