What is the significance of making a sheet and selling it?
Rashi (31, according to the Mashal): Torah gives glorious clothing to Chachamim.
Malbim (Derech ha'Muskal): This is the garment that she wove via the ways of Binah. It weaves ideas one to another. Binah is compared to business - "u'Knos Binah Nivchar mi'Kasef" (16:16). Also, se teaches the ways of her Binah to others, and gains from this - 'I learned much from my Talmidim more than from all of them (my Rebbeyim and colleagues)' (Ta'anis 7a).
What is "Kena'ani"?
Rashi: It is a merchant.
What is the significance of giving a belt to a merchant?
Rashi (31, according to the Mashal): Because he is girded with business [of Torah], it gives to him a belt for his loins.
Malbim (Derech ha'Muskal): A belt is conduct between good and evil, based on Chachmah. It is compared to a belt, which girds the loins with strength. So Chachmah overpowers the Yetzer to do valiantly. She gave this to a merchant, so others will learn this from her deeds.