1)
How will we reconcile this Pasuk with the Mishnah in Avos, 1:3, 'Al Tih'yu ka'Avadim ha'Meshamshin es ha'Rav Al-M'nas Lekabel P'ras'?
1.
Seforno: The Torah is merely stating that the Mitzvos they would perform when rosssing the Yarden - with regard to the various sets of stones that they rected, and on which they wrote the entire Torah as testimony ... , will ensure that their children go on the right path and will live a long time in the land.
2.
Da'as Zekenim and Hadar Zekenim: We should perform Mitzvos out of love, and the Torah is informing us here that it is in order to do so that we will inheri the land.
