Sforno on Genesis 49:15/ספורנו על בראשית מ״ט:ט״ו

1וירא מנוחה כי טוב, by pursuing his twin objectives he found true מנוחה, i.e. a kind of being at peace with oneself knowing one has done what is expected of one. The prophet Jeremiah 6,16 describes such a state of mind as ומצאו מרגוע לנפשותיכם, “find tranquility for yourselves.” [He advised people of his time to travel ancient paths, i.e. the path of Torah as it used to be practiced. Ed.]

2ואת הארץ כי נעמה he found that the land he inhabited provided his livelihood without strenuous effort on the part of its inhabitants.

3ויט שכמו לסבול, he accepted two kinds of burdens, the yoke of Torah and the yoke of public service. This reflects what our sages have said in Moed Katan 6 that young Torah scholars have to accept the burdens of their entire town upon themselves.

4ויהי למס עובד, the general population which carries out the day-to-day mundane tasks involved in a civilised existence will be at the disposal of Issachar who is busy with Torah study instead. The word מס refers to the ordinary working man doing the chores of Issachar being viewed as the tax being paid on behalf of Issachar, seeing that he himself cannot be taxed on non-earned income. In halachah, (Yumah 72) this is described as the ordinary citizen having to perform public service duties from which the Torah scholars are excused.