“In the third month after the exodus of the Children of Israel from the land of Egypt, on this day, they came to the Sinai desert.”1בַּחֹדֶשׁ הַשְּׁלִישִׁי לְצֵאת בְּנֵי יִשְׂרָאֵל מֵאֶרֶץ מִצְרָיִם בַּיּוֹם הַזֶּה בָּאוּ מִדְבַּר סִינָי,
From this verse, our Sages derive that our ancestors entered the Sinai desert on Rosh Chodesh Sivan in preparation for the Giving of the Torah, as the Gemara states,2 “This verse states, ‘On this day (bayom hazeh), they came to the Sinai desert,’וְאִיתָא בַּגְּמָרָא, כְּתִיב הָכָא בַּיּוֹם הַזֶּה בָּאוּ מִדְבַּר סִינָי
and elsewhere, it is written,3 ‘This month (hachodesh hazeh) will be for you the beginning of the months.’וּכְתִיב הָתָם הַחֹדֶשׁ הַזֶּה לָכֶם רֹאשׁ חֳדָשִׁים,
Just as the latter verse refers to Rosh Chodesh, so too is the former verse referring to Rosh Chodesh,” the birth of the new moon.4מַה לְּהַלָּן רֹאשׁ חֹדֶשׁ אַף כָּאן רֹאשׁ חֹדֶשׁ.
The Talmud is employing the principle of exegesis known as gezeirah shavah5 to teach that the Children of Israel arrived at the Sinai desert on Rosh Chodesh.
Tosafos raise a question regarding this teaching, suggesting that it would have been preferable to derive this concept from another source:6 In Tractate Pesachim7 (concerning the verse,8 “G‑d spoke to Moshe in the Sinai desert in the second year… in the first month”);וְהִקְשׁוּ בַּתּוֹסְפוֹת, בִדֶּבְּמַסֶּכֶת פְּסָחִים אִיתָא (עַל הַפָּסוּק וַיְדַבֵּר ה' אֶל מֹשֶׁה בְמִדְבַּר סִינַי בַּשָּׁנָה הַשֵּׁנִית גו' בַּחֹדֶשׁ הָרִאשׁוֹן),
our Sages derive that the verse is referring to Rosh Chodesh through the same principle of exegesis, but based on a different word, the word midbar, “desert,” that is used in two verses.אָתְיָא מִדְבָּר מִמִּדְבָּר,
In the verse under discussion, it is written, “In the Sinai desert,”כְּתִיב הָכָא בְּמִדְבַּר סִינַי
and in another verse, it is written,9 “G‑d spoke to Moshe in the Sinai desert, in the Tent of Meeting, on the first of the second month.”וּכְתִיב הָתָם וַיְדַבֵּר ה' אֶל מֹשֶׁה בְּמִדְבַּר סִינַי בְּאֹהֶל מוֹעֵד בְּאֶחָד לַחֹדֶשׁ הַשֵּׁנִי,
Just as the latter verse is referring to Rosh Chodesh,10 so too is the former verse referring to Rosh Chodesh.מַה לְּהַלָּן בְּרֹאשׁ חֹדֶשׁ אַף כָּאן בְּרֹאשׁ חֹדֶשׁ,
Tosafos ask: Since the verse “In the third month…” also contains the word midbar, “desert,”וְכֵיוָן שֶׁגַּם בַּפָּסוּק בַּחֹדֶשׁ הַשְּׁלִישִׁי כְּתִיב מִדְבָּר,
why didn’t our Sages derive that this verse, too, is referring to Rosh Chodesh on the basis of the gezeirah shavah stemming from the use of the word midbar in both verses?אַמַּאי לֹא יָלִיף הָכָא מִדְבָּר מִמִּדְבָּר.
Tosafos’ question requires explanation:וְצָרִיךְ לְהָבִין,
Seemingly, the derivation of the meaning of the verse through the gezeirah shavah based on the use of the word hazeh is preferable, for it demonstrates that the meaning of the phrase bayom hazeh is Rosh Chodesh.דְּלִכְאוֹרָה, הַיַּלְפוּתָא מֵהַגְּזֵרָה שָׁוָה הַזֶּה הַזֶּה מְגַלֶּה שֶׁפֵּרוּשׁ בַּיּוֹם הַזֶּה הוּא בְּרֹאשׁ חֹדֶשׁ,
If, in contrast, the reference to Rosh Chodesh would be derived through the gezeirah shavah based on the use of the word midbar,מַה שֶּׁאֵין כֵּן בְּאִם הָיוּ לְמֵדִין מֵהַגְּזֵרָה שָׁוָה מִדְבָּר מִדְבָּר
[in which instance the gezeirah shavah would teach only that the event mentioned in the verse (the Jews’ arrival at the Sinai desert) took place on Rosh Chodesh],[שֶׁהַלִּמּוּד הוּא רַק שֶׁהָעִנְיָן שֶׁנֶּאֱמַר בַּכָּתוּב (בָּאוּ מִדְבַּר סִינָי) הָיָה בְּרֹאשׁ חֹדֶשׁ]
then the meaning of the phrase bayom hazeh would not be understood as explicitly referring to Rosh Chodesh.לֹא הָיָה מוּבָן הַפֵּרוּשׁ דְּבַיּוֹם הַזֶּה
In contrast to the gezeirah shavah based on the word midbar, the gezeirah shavah based on the word hazeh focuses on the meaning of the phrase bayom hazeh, “on this day,” defining the day itself as Rosh Chodesh.
[There is an additional advantage to the gezeirah shavah based on the word hazeh over the gezeirah shavah based on the word midbar:[וְעוֹד יִתָּרוֹן בְּהַגְּזֵרָה שָׁוָה הַזֶּה הַזֶּה עַל הַגְּזֵרָה שָׁוָה מִדְבָּר מִדְבָּר,
For the meaning of the phrase hachodesh hazeh is Rosh Chodesh;11 that is the intent of the word itself that forms the basis of the gezeirah shavah.כִּי הַחֹדֶשׁ הַזֶּה פֵּרוּשׁוֹ הוּא רֹאשׁ חֹדֶשׁ,
By contrast, in the other phrase, bamidbar Sinai, “the Sinai desert,” the term that serves as the basis of that gezeirah shavah, and “on the first of the month, (which refers to Rosh Chodesh), are two discrete matters.]12מַה שֶּׁאֵין כֵּן מִדְבַּר סִינַי וְאֶחָד לַחֹדֶשׁ (רֹאשׁ חֹדֶשׁ) הֵם שְׁנֵי עִנְיָנִים],
What, then, is the basis for Tosafos’ reasoning that the interpretation of the verse should have been derived from the gezeirah shavah based on the word midbar?13וּמַהִי סְבָרַת הַתּוֹסְפוֹת דַּהֲוָה לֵיהּ לְמֵילַף מִדְבָּר מִמִּדְבָּר.

Summary

Our Sages derive that the phrase “on this day” in the verse “In the third month after the exodus of the Children of Israel from the land of Egypt, on this day, they came to the Sinai desert,” refers to Rosh Chodesh, based on a gezeirah shavah that associates the above verse with the verse, “This month will be for you the beginning of the months.” In their gloss to this passage, Tosafos raise a question, stating that it seemingly would have been preferable to derive that concept from a gezeirah shavah based on the verse “G‑d spoke to Moshe in the Sinai desert in the Tent of Meeting, on the first of the month.”
Tosafos’ question is problematic because there is an obvious advantage to the gezeirah shavah based on the verse, “This month will be for you the beginning of the months.” It reveals that the meaning of the term “this day” itself is Rosh Chodesh. What, then, is the basis for Tosafos’ question?