Yissachar-Ohr Hachaim Hakadosh – Vayechi
“He saw tranquility that it was good, and the land that it was pleasant, yet he bent his shoulder to bear and he became an indentured servant.” (Genesis 49:15) Issachar correctly evaluates the repose in the World to Come as well as the relative pleasantness on earth. When Jacob added, “He bent his shoulder to bear,” this is a reference to the pain that is part of our earthly existence. “He turned himself,” into someone who serves the Lord as a form of paying tribute.
Another meaning of these last words may be that in return for becoming a willing servant of the Lord, the rest of the population is obligated to pay a tax to assure the Torah scholar of his livelihood.
In the case of Issachar that would be Zebulun who was a seafarer putting much of his wealth at the disposal of Issachar.