Rashi on Deuteronomy
השמר לך TAKE HEED TO THYSELF [LEST THOU FORSAKE THE LEVITE] — This is intended in addition to the positive command expressed in the previous verse, to attach to it (the neglect of the Levite) a negative command, also.
Rashbam on Deuteronomy
כל ימיך על אדמתך, for all the years that you dwell in your land.
Rabbeinu Bahya
כל ימיך על אדמתך, “all your days on your land.” The specific command not to abandon the Levite is applicable only in the Holy Land. Levites in the Diaspora do not enjoy preferred status regarding receipt of charity from their brethren.