In our Gemara on Amud Beis tells us that according to one opinion the Jews of the wilderness could not undergo circumcision due to the travails of traveling, which would endanger their lives post operatively.

Ritva asks, why was Moshe punished for not circumcising Eliezer, since he was traveling and could not endanger Eliezer anyhow? Ritva answers that Moshe could have paused on his journey and waited several days until Eliezer recovered, as though God commanded him to return to Egypt, he was not given a specific time frame and could have done the circumcision first

This Ritva is difficult to understand because how could Moshe have presumed to delay God’s command to return to Egypt in deference to the command of circumcision?  Logically speaking, a more specific immediate command should take precedence, otherwise God should have said, “Take care of the circumcision BEFORE you go back to Egypt.” In the absence of that, it would seem more reasonable to follow the specific and therefore timely directive to return to Egypt.  In fact, Shita Mekubetzes (Nedarim 31b) raises this exact issue.

Let us study the original sugya that is found in Nedarim (ibid):

תַּנְיָא רַבִּי יְהוֹשֻׁעַ בֶּן קׇרְחָה אוֹמֵר גְּדוֹלָה מִילָה שֶׁכׇּל זְכִיּוֹת שֶׁעָשָׂה מֹשֶׁה רַבֵּינוּ לֹא עָמְדוּ לוֹ כְּשֶׁנִּתְרַשֵּׁל מִן הַמִּילָה שֶׁנֶּאֱמַר וַיִּפְגְּשֵׁהוּ ה׳ וַיְבַקֵּשׁ הֲמִיתוֹ

It is taught in a baraisa that Rabbi Yehoshua ben Korḥa says: So great is the mitzva of circumcision that all the merits that Moses our teacher accrued when he performed mitzvot did not protect him when he was negligent about performing the mitzva of circumcision, as it is stated: “And the Lord met him and sought to kill him” (Exodus 4:24).

אָמַר רַבִּי חַס וְשָׁלוֹם שֶׁמּשֶׁה רַבֵּינוּ נִתְרַשֵּׁל מִן הַמִּילָה אֶלָּא כָּךְ אָמַר אָמוּל וְאֵצֵא סַכָּנָה הִיא שֶׁנֶּאֱמַר וַיְהִי בַיּוֹם הַשְּׁלִישִׁי בִּהְיוֹתָם כֹּאֲבִים וְגוֹ׳ אָמוּל וְאֶשְׁהֶא שְׁלֹשָׁה יָמִים הַקָּדוֹשׁ בָּרוּךְ הוּא אָמַר לִי לֵךְ שֻׁב מִצְרָיִם אֶלָּא מִפְּנֵי מָה נֶעֱנַשׁ מֹשֶׁה

Rabbi Yehuda HaNasi said: Heaven forbid that Moses our teacher was neglectful of the mitzva of circumcision. Rather, this is what he said: If I circumcise the child now and depart to begin my journey, it is a danger for the child, as it is stated: “And it came to pass on the third day, when they were in pain” (Genesis 34:25), which indicates that the pain of circumcision lasts for several days and the child may be in danger while in pain. If I circumcise him immediately and wait three days and only then embark on the journey, this is problematic, as the Holy One, Blessed be He, said to me: “Go, return into Egypt” (Exodus 4:19), i.e., go immediately. For these reasons Moses did not circumcise the child immediately, but no neglect existed on his part. But according to this explanation, for what reason was Moses punished?

מִפְּנֵי שֶׁנִּתְעַסֵּק בַּמָּלוֹן תְּחִלָּה שֶׁנֶּאֱמַר וַיְהִי בַּדֶּרֶךְ בַּמָּלוֹן

Because he was occupied with lodging first and did not immediately perform the mitzva of circumcision, as it is stated: “And it came to pass on the way at the lodging-place” (Exodus 4:24).

In a simple reading of the text, we can assume that Rabbi Yehoshua ben Karcha argued with Rabbi Yehuda HaNasi. Rabbi Yehoshua ben Karcha faulted Moshe for delaying the Bris, and Rabbi Yehuda HaNasi says, Moshe couldn’t have been merely procrastinating but instead was justifiably worried about the travel, and only was punished for focusing on setting up lodging before focusing on the Bris. (The lodging was close enough to Mitzrayim that the travails of traveling would no longer be a danger to the child, see commentary of Rosh Nedarim Op. Cit.) 

We therefore must say that Ritva was asking only according Rabbi Yehoshua ben Karcha, because according to Rabbi Yehuda HaNasi, in fact,  Moshe rightfully did not circumcise his son while  traveling.  It was only incumbent upon him once he settled at the inn close to Egypt, where there was no longer concern of travel-related stress and dangers (see Rosh, Op. Cit.). Perhaps the dispute between Rabbi Yehuda HaNasi and Rabbi Yehoshua ben Karcha, according to the Ritva, was itself whether Moshe should have assumed that the standing obligation of Milah took precedence over a specific command.  

While we are discussing Moshe’s sin, let us survey other interpretations for what was Moshe’s sin and why he was attacked by the angel.  Daas Zekeinim (Shemos 4:24) embellishes the Gemara’s peshat by offering that Moshe delayed and should have done the Bris before dealing with lodging and have left Tziporah at the inn to take care of Eliezerm, while he went on to Egypt.

Chasam Sofer (Shemos 74) offer a completely original explanation, offering the proviso, that he is fearful of saying a different peshat than the Gemara. He suggests that In truth, Moshe was correct and did not err at all in delaying the circumcision since it was dangerous.  His problem was that he inadvertently caused a Chillul Hashem in that he did not explain to Tziporah his motives. This led her to believe that he took God’s command lightly. He only told her (Shemos 4:18):

אֵ֣לְכָה נָּ֗א וְאָשׁ֙וּבָה֙ אֶל־אַחַ֣י אֲשֶׁר־בְּמִצְרַ֔יִם וְאֶרְאֶ֖ה הַעוֹדָ֣ם חַיִּ֑ים וַיֹּ֧אמֶר יִתְר֛וֹ לְמֹשֶׁ֖ה לֵ֥ךְ לְשָׁלֽוֹם׃

Moses went back to his father-in-law Jether* and said to him, “Let me go back to my kinsfolk in Egypt and see how they are faring.”* And Jethro said to Moses, “Go in peace.”

This gave the impression that Moshe was on a private mission.  So Tziporah saw Moshe as not taking circumcision and God’s command seriously.  Chasam Sofer adds, this is why Tziporah went back to Midyan.  Why should she risk her life for Moshe’s personal junket? Later on, Yisro sends Tzipporah back, because after the Exodus, Yisro (and Tzipporah) realized that Moshe was on a divine mission.  This is how Chasam Sofer reads this verse(Shemos 181-2):

וַיִּשְׁמַ֞ע יִתְר֨וֹ כֹהֵ֤ן מִדְיָן֙ חֹתֵ֣ן מֹשֶׁ֔ה אֵת֩ כׇּל־אֲשֶׁ֨ר עָשָׂ֤ה אלוקים לְמֹשֶׁ֔ה וּלְיִשְׂרָאֵ֖ל עַמּ֑וֹ כִּֽי־הוֹצִ֧יא ה׳ אֶת־יִשְׂרָאֵ֖ל מִמִּצְרָֽיִם

Jethro priest of Midian, Moses’ father-in-law, heard all that God had done for Moses and for Israel, God’s people, how Hashem had brought Israel out from Egypt.

וַיִּקַּ֗ח יִתְרוֹ֙ חֹתֵ֣ן מֹשֶׁ֔ה אֶת־צִפֹּרָ֖ה אֵ֣שֶׁת מֹשֶׁ֑ה אַחַ֖ר שִׁלּוּחֶֽיהָ׃

So Jethro, Moses’ father-in-law, took Zipporah, Moses’ wife, after she had been sent home. That is, after Yisro realized that Moshe was on a divine mission and was following God’s orders, then Yisro sent Tziporah back to him.

A lesson we see from here is that even though it is good to be modest and humble, and especially the righteous “say little and do much”, they should share with their family members their motivations and aspirations, otherwise how would they know?