They shall assemble at Mount Moriah, etc. Meaning, at the pilgrimage festivals. You might ask: If so it should have said assemble and not invited. Therefore Rashi explains, Every assembly is through invitation, etc. Therefore, even though [the assembly] here is not by invitation, rather they came on their own, the verse still writes an expression of "invitation." Re"m writes, My heart is dissatisfied with this [explanation] because יקראו should have been written with a kamatz under the קוף and the ריש with a tzeirei to make it reflexive. [Whereas according to the punctuation of our verse, יקראו means 'they assemble them,' wrongly implying that Yisachar and Zevulun assemble the people]. It seems to me that אסיפה here means inviting as we explained, and [the active conjugation means not that Yisachar and Zevulun assemble them, but that] they assemble on their own to fulfill Hashem's commandment to come up on pilgrimage festivals. And because other assemblies are by invitation, Scripture here writes יקראו instead of יתאספו. And it is not reflexive and therefore it is not punctuated with reflexive punctuation. (So it seems to me). Re"m further writes, However, I do not know what relevance there is to mentioning the assembling of the tribes at Mount Moriah within the blessing of Yisachar and Zevulun?" In truth, I do not know why he does not know, because [apparently] Rashi himself was aware of this question and he writes, Based on their arrangement of the time [divisions] and of the leap year—'Peoples,' of the tribes of Yisroel, — 'Shall assemble at the mountain,' Mount Moriah, etc. Perhaps Re"m wrote what he wrote because he had a [different] erroneous text. This is easy to understand. (So it seems to me).
And there slaughter, during the festivals, righteous offerings. Rashi wants to show the connection between the verses. Therefore he adds a vav [and] to indicate that they will [all] slaughter righteous offerings on the festivals, even though they bring offerings there every day of the year. Therefore Rashi adds and in order to connect the phrases of the verse together.
Affording them the opportunity, etc. Rashi explains, what blessing is there in this [unless they can study Torah]?
טרית (tuna). טרית is a kind of fish named tunina.
Zevulun, a people disdainful of their souls in seeking death, etc. It is talking about Zevulun there, who wished death for himself because Naftoli was on the loftiest ground. The Gemara asks on this [verse]: A people disdainful of their souls, that just because Naftoli was on the loftiest ground he should seek death for himself? The Gemara answers, Zevulun lamented, etc. and to me you only gave seas. The Holy One, Blessed Is He answered him, To you I gave the sea from where you can take tuna, etc.
Translated by Targum as "lined with a cedar covering." Meaning that it covers the beams with cedar.
Another interpretation. "Gentile nations shall assemble at the mountain, etc." Because according to the first interpretation you might ask why it says There will they slaughter righteous offerings, are not all offerings slaughtered there? Also, what is [the meaning of] righteous offerings? Are not all offerings [wherever they are permitted] righteous offerings? Therefore he gives another interpretation, etc. And according to the other interpretation too, you might ask that it should have said explicitly [that they at least retract from idolatry], because before bringing offerings they need conversion, [retraction] from their idolatry! Therefore he also needs the first interpretation.