Commentary for Numbers 15:2

כי תבאו WHEN YE ARE COME [INTO THE LAND] — He brought them the good tidings that they would enter the land.

WHEN YE ARE COME INTO THE LAND OF YOUR HABITATIONS. After He had assured the children [of those who had left Egypt] that they would come into the Land,¹⁷⁶Above, 14:31. He completed [telling] them the laws of the offerings, and that they should bring the drink-offerings when they enter the Land. Perhaps this [section] was [told to them] now in order to console them and give them an assurance [that they would indeed take possession of the Land], for they began to give up hope, saying: “Who knows what will happen in such a long time — after forty years — for may be the children will also sin?” Therefore the Holy One, blessed be He, saw fit to comfort them, for by commanding them precepts which are applicable [only] in the Land, He thereby was assuring them that it is clearly destined by Him that they will come into and inherit the Land.
Now He commanded them concerning the drink-offerings [that they were to bring] in the Land when making burnt-offerings and peace-offerings, since in the wilderness they had no duty to bring drink-offerings except with the continual [daily] burnt-offering, concerning which it is said, and the fourth part of a hin of wine for a drink-offering for the one sheep;¹⁷⁷Exodus 29:40. for there it is said [that it be brought continually every day] at the door of the Tent of Meeting before the Eternal, where I will meet with you, to speak there unto thee.¹⁷⁸Ibid., Verse 42. Similarly the princes when bringing their dedication-offerings¹⁷⁹Above, 7:12-83. did not include amongst them drink-offerings.
Now our Rabbis differed on this matter. Some of them said in the Sifre¹⁸⁰Sifre, Shelach 107. that Scripture here teaches us that they only became obliged to bring drink-offerings from the time that they came into the Land onwards etc.; but some of them said that it is [only] the individual who was not obliged to bring drink-offerings [together with his offering] until they entered the Land [but public offerings were always accompanied by drink-offerings].
He also completed [here] the laws relating to the priests by commanding the [duty of the] dough-offering,¹⁸¹Further, Verses 17;21. which was not applicable in the wilderness, for it was already known that the heave-offering and the tithes do not apply there, since such produce was winnowed by non-Jews and [grown] outside the Land of Israel. There is also a difference in the opinion of the Rabbis¹⁸²Sifre, Shelach 110. concerning the [law of the] dough-offering [which is different from that of tithes etc.], namely that they became subject to the law of the dough-offering as soon as they entered the Land, but were not liable to [separate] tithes and the heave-offering until after [the fourteen years of] the conquest and settlement [of the Land].

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.