1. Baal HaTurim has a bunch of derivations for the 39 melachos in the beginning, some more farfetched than others. What is the motivation here? Because there is no clear derivation of these 39 from the text, and giving repeated hints to the idea from the text shows that it is there beneath the surface. Chazal made such derashot here as well.
Avakesh claims that this gematria is peshat, because of other deductions that can be made at the spot, namely of connections between the Mishkan and Shabbat. I am not certain I agree with the particulars but do agree somewhat with the general thought, of a peshat derivation which leads to the same conclusions as the memorable derash, and I have given examples of this in the past.
It could also be that the definition of melacha was left ambiguous, and as it was shaped and understood by its interpreters, so became its definition, on a DeOrayta level.
2) Rashi on Vayahkel says it is the hiphil, because Moshe did not gather with his hands but caused them to gather together via speech. He reinforces his point with a quote from Onkelos which uses the aphel form. I posted on this in the past, just explaining the Rashi.
Mizrachi is bothered by some aspects of this Rashi. What is Rashi's motivation here? Why focus on this hiphil? Why on this word? Does it ever occur in a different pattern? What about the command "gather" no in hiphil which was presumably done via dibbur? And why when gathering 70 zekeinim, after a command to gather, we have:
וַיֶּאֱסֹף שִׁבְעִים אִישׁ, מִזִּקְנֵי הָעָם, וַיַּעֲמֵד אֹתָם, סְבִיבֹת הָאֹהֶל
where it is the kal rather than hiphil (and I would note, so too in Targum Onkelos).
And so on. I am not doing it justice, so read it all inside.
None of this really bothers me. This is the first word of the sidra, and is the name of the sidra, so it certainly can merit discussion. And it can also draw attention because of location, location, location early on the parsha. Just as an analysis of groups of names, with and without vav hachibbur in various places, might be appropriate for Ibn Ezra to discuss in the beginning of Shemot, where it is more prominent. And Rashi pays attention to Onkelos and takes his lead, so this might have also been a factor.
I would read it as this being allowed to take the form of hiphil, and making sense in that context, because it means "cause them to gather themselves." But other forms, such as gathering in kal are not disallowed.
Meanwhile, this is also the subject of conversation by others. Shadal, in his work, Ohev Ger, has more of a focus on Onkelos, which also factors into this. Shadal writes in Ohev Ger what is pictured to the right.
It is interesting indeed that Rashi's support/impetus in Onkelos may not even be there. For in most text, it is Kal rather than Aphel.
Meanwhile, in parshat Korach, on the pasuk וַיַּקְהֵל עֲלֵיהֶם קֹרַח אֶת-כָּל-הָעֵדָה, אֶל-פֶּתַח אֹהֶל מוֹעֵד, it is Aphel in most (but not all) manuscripts. This perhaps makes sense, as we have three actors, and Korach caused the people to gather before Moshe; and we also have the derasha of Vayikach Korach as with Devarim.
Shadal would remove the Aphel from all places, and leave it as kal. I am not entirely persuaded. But it is an interesting topic.
The image above also had the text of Rashi, and the text of Siftei Chachamim, pulled from an online Mikraos Gedolos. I will repeat the image here.
Sifsei Chachamim cites Mizrachi who does not understand Rashi's motivation. In response, Sifsei Chachamim suggests that it is this girsalogical difference in Onkelos here, and in parshat Korach, which is motivating Rashi to make his comment here, to establish the correct girsa in Onkelos. I am not persuaded; I would still see the reference to Onkelos as an appeal to authority rather than the ultimate aim of Rashi commentary on this word.
Now often, in Mikraos Gedolos, and elsewhere, there are "rules for understanding Rashi," which explain what Rashi means when he cites Onkelos, based on whether Rashi uses the word targumo, or veOnkelos tirgem, and so on. Not that I think that these general rules are always right, but what do they say for the word used here veTargumo?