“It shall be when you come into the land of Israel, you shall take from your first fruits and bring them to the Temple”
Our tradition explains that the Torah is making the connection that by performing this Misva of bringing the first fruits we will be deserving to dwell in the land.
During the 40 years in the desert, with the heavenly manna that descended daily from heaven, all their needs were being divinely provided for. Therefore, the people were free to engage in their spiritual development. Entering the promised land was going to bring about a radical change. There would be no more free lunch and people would have to till the land, plow, plant, irrigate, fertilize, harvest, winnow, grind grain, and bake in order to nourish themselves. There would have to be trade and commerce, and a myriad of activities that would greatly distract them from the study of Torah.
Why, then, enter the land? Would it not be better to remain in their miraculous existence and be free to devote themselves to their spiritual growth?
G-d‘s Will was to have the Torah observed on earth, with human actions of working the land according to the dictates of Torah law, and engaging in trade according to the moral laws of the Torah. Moreover, it is Man’s responsibility to transform the physical world we live in and infuse it with a higher purpose and this can be achieved only through using the physical world in performance of Misvot and so the forty year sojourn in the desert was the preparation for when the real work would begin and that was when they entered the real world.