Or HaChaim on Numbers 15:2/אור החיים על במדבר ט״ו:ב׳

1 כי תבואו אל ארץ מושבותיכם, "when you will come to the land of your habitations, etc." When G'd saw the despondency of the Jewish people over the decree that He had issued against them to wander aimlessly in the desert for forty years, He provided some encouragement for their hearts by instructing them in commandments which would apply only once they lived in the land of Canaan. G'd wanted to keep this prospect before their eyes in order to make their lives more meaningful. If one knows that at the end of a certain period of time one will experience fulfilment of one's hopes then the time lag until then becomes less onerous. G'd made sure to write אשר אני נותן לכם, "which I am about to give to you," although the generation He addressed had already been described as carcasses. He taught the people that the accomplishments of the children reflect credit also on their parents seeing the children are meant to be the extension of their parents.

2Another reason why the Torah wrote here נותן לכם, "am about to give you," may be based on Sanhedrin 90 where the Talmud raises the question "where it is written in the Torah that there will be a resurrection?" The Talmud quotes Exodus 6,4: "and I will also keep My covenant with them (the patriarchs) to give the land of Canaan to them." The fact that the Torah did not write "to you," seeing the living Israelites were being addressed, proves that the patriarchs will be resurrected. In our verse the Torah addresses "carcasses." The verse makes sense only if it presumes that these "carcasses" will be resurrected and will take possession of their land.