Rashi on Deuteronomy 33:18/רש"י על דברים ל״ג:י״ח

1ולזבולן אמר AND OF ZEBULUN HE SAID — These five tribes whom he blessed last, Zebulun, Gad, Dan, Naphtali and Asher, it repeats their names in order to instil them with strength and power, because they were the weakest of all the tribes. They are the very same whom Joseph took to Pharaoh, as it is said, (Genesis 47:2, cf. Rashi thereon) “And of the least of his brothers he took five men [and placed them before Pharaoh]” — because these looked weak, so that he (Pharaoh) should not appoint them his war officers (Bava Kamma 92a).

2שמח זבולן בצאתך ויששכר באהליך REJOICE, ZEBULUN. IN THY GOING OUT, AND, ISSACHAR, IN THY TENTS — Zebulun and Issachar entered into a partnership: Zebulun dwelt at the harbour of ships and went out in ships to trade; he made profit and used to provide food for Issachar who sat at home and occupied themselves with the Torah. Consequently he mentioned Zebulun before Issachar (although the latter was the elder) because Issachar’s knowledge of Torah was due to Zebulun (Genesis Rabbah 99:9).

3שמח זבולן בצאתך REJOICE, ZEBULUN, IN THY GOING FORTH — Be successful when thou goest out to trade,

4ויששכר AND ISSACHAR, be successful when you sit in your tents (באהליך) to study the Torah — to sit in the Sanhedrin and to intercalate the years and to fix the day of New Moon, as it is said, (I Chronicles 12:33) “And of the children of Issachar, men that had understanding of the times, … the heads of them were two hundred”: as the heads of the Sanhedrin they used to busy themselves with this (Genesis Rabbah 72:5), and in accordance with their fixing of the seasons and their calculation of intercalary years,