Why should the half-shekel perplex Moshe Rabbenu?

That's Greek ...
er, Paelo-Hebrew ...
to me!

Summary: Maybe it did not. But why it might have.

Post: In the beginning of Ki Tisa {30:13}, Moshe is instructed that when counting the Israelites, each one should give a half-shekel.

13. This they shall give, everyone who goes through the counting: half a shekel according to the holy shekel. Twenty gerahs equal one shekel; half of [such] a shekel shall be an offering to the Lord.		יג. זֶה יִתְּנוּ כָּל הָעֹבֵר עַל הַפְּקֻדִים מַחֲצִית הַשֶּׁקֶל בְּשֶׁקֶל הַקֹּדֶשׁ עֶשְׂרִים גֵּרָה הַשֶּׁקֶל מַחֲצִית הַשֶּׁקֶל תְּרוּמָה לַי־הֹוָ־ה:
This they shall give -- He showed him a coin of fire, and its weight was half of a shekel, and He said to him "like this shall they give."		זה יתנו: הראה לו כמין מטבע של אש, ומשקלה מחצית השקל, ואומר לו כזה יתנו:

This derasha is found in Midrash Tanchuma on the parasha:

זה יתנו 

אמר רבי מאיר:
כמין מטבע של אש הוציא הקדוש ברוך הוא מתחת כסא הכבוד והראהו למשה ואמר לו: זה יתנו, כזה יתנו. 

Mekorei Rashi gives many sources for this statement. See starting with footnote daled:

This is a derasha on the word zeh, which is oft taken to refer to something you can point to.

Sometimes, there are lists of such items that Hashem showed to Moshe. Thus, in Menachot 29a:

רבי יוסי ברבי יהודה אומר ארון של אש ושלחן של אש ומנורה של אש ירדו מן השמים וראה משה ועשה כמותם שנאמר (שמות כה, מ) וראה ועשה כתבניתם אשר אתה מראה בהר אלא מעתה (שמות כו, ל) והקמת את המשכן כמשפטו אשר הראית בהר הכי נמי הכא כתיב כמשפטו התם כתיב כתבניתם 

א"ר חייא בר אבא אמר ר' יוחנן גבריאל חגור כמין פסיקיא היה והראה לו למשה מעשה מנורה דכתיב וזה מעשה המנורה 

תנא דבי רבי ישמעאל שלשה דברים היו קשין לו למשה עד שהראה לו הקב"ה באצבעו ואלו הן מנורה וראש חדש ושרצים מנורה דכתיב (במדבר ח, ד) וזה מעשה המנורה ראש חודש דכתיב (שמות יב, ב)החודש הזה לכם ראש חדשים שרצים דכתיב (ויקרא יא, כט) וזה לכם הטמא ויש אומרים אף הלכות שחיטה שנאמר (שמות כט, לח) וזה אשר תעשה על המזבח:

Making use of the Point by Point Summary for a ready translation:

(p) (Beraisa - R. Yosi b'Rebbi Yehudah): Fiery forms of the following Kelim descended from Shamayim, Moshe saw them and (taught Betzalel, who) made them - the Aron, Shulchan and Menorah - "U'R'e va'Ase b'Savnisam Asher Hareisa ba'Har".
(q) Question: If so, we should likewise expound "Va'Hakemosa Es ha'Mishkan k'Mishpato Asher Hareisa ba'Har" to teach that a fiery form of the Mishkan descended from Shamayim!
(r) Answer: No - regarding the Mishkan it says "k'Mishpato" (connoting that Moshe received its Halachos), regarding the Kelim it says "b'Savnisam" (connoting that he saw its form.)
(s) (R. Chiya bar Aba): Gavri'el descended and showed Moshe how to make the Menorah - "V'Zeh Ma'ase ha'Menorah".
(t) (Beraisa - Tana d'vei R. Yishmael): Moshe had difficulty understanding three things, until Hash-m showed him (as vividly as) with a finger - the Menorah, Rosh Chodesh and Sheratzim;

1. We learn from "V'Zeh Ma'ase ha'Menorah", "Ha'Chodesh ha'Zeh Lachem Rosh Chadashim", and "V'Zeh Lachem ha'Tamei".
2. Some say, he also showed him laws of (i.e. where is the valid place for) slaughter - "V'Zeh Asher Ta'aseh Al ha'Mizbe'ach" (slaughter is the first part of Hakravah.)

Thus, from the give and take of the gemara, this appears to be a closed list. Yet other items are added on the basis of veZeh.

The gemara in Chullin 42a reads:

ואידך האי זאת מאי עביד ליה מיבעי ליה לכדתנא דבי רבי ישמעאל דתנא דבי רבי ישמעאל זאת החיה אשר תאכלו מלמד שתפס הקב"ה מכל מין ומין והראה לו למשה ואמר לו זאת אכול וזאת לא תיכול

Or, in English, a summary:

(h) Answer #1: "*This* is the Chayah you may eat" - implying, there is another Chayah (living animal) you may not eat, namely a Tereifah.

1. Our Tana expounds "This" like Tana d'Vei R. Yishmael.

i. (Beraisa - Tana d'Vei R. Yishmael): "*This* is the Chayah you may eat" - Hash-m showed Moshe every species and told him which may be eaten.

Tosafot on these two gemaras read as follows. In Menachos, where it is clear that there was a difficulty to Moshe in these three things, they write:

שלשה דברים היו קשין לו למשה כו'. ואם תאמר וליחשוב נמי ההיא דאלו טריפות (חולין דף מב.) דאמר וזאת החיה אשר תאכלו מלמד שתפס הקב"ה כל מין ומין והראה לו למשה ואמר לו זאת אכול וזאת לא תאכל ויש לומר דלא חשיב אלא הך דכתיב זה ויש לתמוה דלא חשיב מחצית השקל דכתיב זה יתנו ואמרינן (שקלים דף ג ומ"ר) כמין מטבע של אש הראהו למשה ויש לומר דלא שייך התם נתקשה אלא משום דלא הוה ידע בשום ענין אם לא היה מראהו. מ"ר:

That is, the reason the example in Chullin, of showing the kosher wild animals to Moshe, is not amongst these three is that these three are zeh, while that is zot. (I would have said that this is not necessarily something that was difficult and perplexing for Moshe. After all, even in Menachot, another brayta lists other forms of vessels of the Mishkan which appeared to Moshe which are not among the three.) Tosafot further asks why the Midrash regarding the half-shekel, זֶה יִתְּנוּ, is not listed, if Hashem showed him the form of a fiery coin. His answer is that this is not something that was perplexing, but just that there was no other way Moshe could have known what it should look like if Hashem didn't show it to him.

Tosafot in Chullin write:

זאת החיה מלמד שתפס הקב"ה כל מין ומין והראה למשה. והא דלא חשיב ליה בהקומץ רבה (מנחות דף כט.) גבי שלשה דברים שנתקשה משה מנורה ראש חדש ושרצים ולא חשיב נמי הא דאמר במדרש כמין מטבע אש הראה הקדוש ברוך הוא למשה דכתיב זה יתנו שמא לא חשיב אלא מידי דנתקשה אבל הני אע"פ שהראהו לא נתקשה בהן אלא שתמה על הדבר מה יוכל אדם ליתן כופר נפשו הראהו הקב"ה להבחין היטב ולהודיע לישראל וכן הכא להראות לישראל איזו היא אסורה ואיזו היא מותרת:

Here, they once again ask why these two were not listed. And in answer, that it was not perplexing in the same way. But read it inside for slight nuanced differences from Tosafot in Menachot, such as perhaps a more philosophical reason for being perplexed, that there can be such a thing as kofer nafsho.

Thus, it does not strike me that there is a need for Moshe Rabbenu to have been perplexed to prompt Hashem showing him the fiery coin. However, I can put forth two reasons for Moshe being confused or at least requiring visual clarification.

1) The pasuk reads זֶה יִתְּנוּ כָּל הָעֹבֵר עַל הַפְּקֻדִים מַחֲצִית הַשֶּׁקֶל בְּשֶׁקֶל הַקֹּדֶשׁ עֶשְׂרִים גֵּרָה הַשֶּׁקֶל מַחֲצִית הַשֶּׁקֶל תְּרוּמָה לַה. What is a shekel here? Is it a weight of precious metal (mishkal) or is it a coin? If it is a coin, the Israelite people were newly minted. Since when do they have coins? Yet this seems to be a Jewish coin, not an Egyptian coin or an Assyrian coin. If so, we need to establish what image is depicted on the obverse and reverse sides. We need to determine its weight and, given its weight, its thickness and its diameter. If Hashem had a specific coin in mind, the easiest way to clarify all these matters is to show an actual example of such a coin.

Related to this, if a shekel and half-shekel of the shekel hakodesh was a known weight, then what is the point of saying עֶשְׂרִים גֵּרָה הַשֶּׁקֶל? Is Moshe really unaware of this basic reality? We can take this as instruction to Moshe who otherwise would NOT have known, or else we could take this as instruction ledoros who might lose track of the weight of the shekel hakodesh, such that we get it as well in another, known unit.

2) There is another reason for Moshe Rabbenu to be perplexed. What in the world is a coin? As I discuss in this parshablog post and then this post, archaeologists claim that coinage was not invented yet. (This presents a problem for some midreshei aggadah that have Avraham and Yaakov minting coins, as well as the traditional understanding of what Avraham paid Efron; and also for a midrash halachah that the pidyon maaser sheni must be done specifically on a coin.) If so, perhaps peshat in this pasuk would be that they were to give bars of precious metal. If this is so, I don't think that Chazal shared this assumption, so this would not really be a reason for them to declare Moshe Rabbenu perplexed.

See Gur Aryeh's lengthy discussion of this Rashi starting here. I don't agree that derashot need to be that systematic, though.