Rashi on Genesis 49:15/רש"י על בראשית מ״ט:ט״ו

1וירא מנחה כי טוב AND HE SAW THAT REPOSE WAS GOOD — He chose (ראה) as his portion a land that was blessed and well-fitted to produce fruits (cf. Onkelos; so that he need not engage overmuch in business.

2ויט שכמו לסבול AND HE INCLINED THE SHOULDER TO RECEIVE THE BURDEN namely the burden of tracking the Torah.

3ויהי AND BECAME unto all Israel his brethren.

4למס עובד A SERVANT UNTO TRIBUTE — deciding for them points of Law and the rules with regard to the fixing of leap-years, as it is said (1 Chronicles 12:32) “And of the children of Issachar, men that had understanding of the times, to know what Israel ought to do; the heads of them were two hundred” — two hundred heads of the Sanhedrin he provided — “and all their brethren were at their commandment” (Genesis Rabbah 99:10).

5ויט שכמו AND HE INCLINED HIS SHOULDER — he lowered his shoulder; similar are, (2 Samuel 22:10) “He bowed (ויט) the heavens” and (Psalms 78:1) “Incline (הטו) your ear”. Onkelos, however, explains it differently: HE BOWED HIS SHOULDER to wage wars and to conquer new districts — for he (Issachar) dwelt on the marches — AND the enemy BECAME subject to him AS A SERVANT TO PAY TRIBUTE.