Numbers 15:2

(When you arrive. He informed them that they would enter the land.)

Speak with the sons of Israel, and say to them: When you have entered into the land of your habitation which I will give you,

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, 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; 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., Verse 42. Similarly the princes when bringing their dedication-offerings did not include amongst them drink-offerings.
Now our Rabbis differed on this matter. Some of them said in the Sifre 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, 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 Rabbis 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 come to the land of your permanent settlement, etc.;” what is the reason that this paragraph has been inserted at this point in the Torah? If anything, the legislation added here would not be applicable for at least another forty years! The people at this stage were so frustrated that they did not believe they would ever get to the Land of Canaan and settle there, as they might become guilty of so many more sins, looking back at the less than two years they had been out of Egypt, and what had befallen them during that short period. The wording of the paragraph, i.e. G–d’s promise to Moses at this point, was meant to reassure them that unless the settlement of the people in their ancestral homeland would become a fact, what would be the point in introducing legislation that is capable of being applied only after they were settled in that land? Moses relayed this legislation to the present generation in order to convince them that their children would definitely become residents of the Holy Land.