When the spies were sent out to Eretz Yisroel, it is written [Bamidbar 13, 20]: It was the season when the first grapes begin to ripen.
The commentators ask: What is the purpose of this information? What is the Torah teaching us?
In the sefer Misbar Kerai, he answers based upon the Rambam (Mechirah 1, 16), who rules that the eating of produce constitutes an acquisition of a field. Accordingly, Moshe instructed the spies to eat from the fruits of the land, for this way, they will be acquiring Eretz Yisroel for the Jewish people.
And, he continues, even according to the Raavad, who disagrees with the Rambam and holds that the eating of produce does not constitute an acquisition of a field, for one must perform an act that is beneficial to the field in order to acquire it, such as locking a door, fencing it or making an opening, even a small amount, nevertheless, here, the eating of the produce would constitute an acquisition. For the Gemora in Bava Basra (119a) states that Eretz Yisroel was regarded as if it was in the possession of the Jewish people (even before the conquest). It therefore follows that a formal act of acquisition was not necessary; they just needed to demonstrate ownership. The Gemora in Pesachim (6b) states: If there are in a man’s field late figs (which will never ripen), and he is guarding his field on account of the grapes (which have not ripened yet); and similarly, if there are late grapes, and he is guarding his field on account of his cucumbers, the halachah is as follows: If the owner is not particular about them, they are not forbidden as theft and are not subject to the halachos of tithing, for ownerless produce is exempt from tithing. Evidently, produce at the end of their season are considered ownerless. If someone would take this produce at that time, he would not be demonstrating ownership at all. This is why the Torah stressed that the spies went at the time when the grapes were beginning to ripen, for then, the eating of the grapes would be demonstrating ownership.