Before the Meraglim went to check out the land, Moshe gave them a number of instructions. One of the things he told them was to check: היש בה עץ אם אין – “If there are any trees or not” (13:20). Rashi explains: “Does it have a worthy man who will protect them with his merit?”.
Why is a worthy man termed a “tree”?
R’ Moshe Sternbuch explains: A tree symbolizes relentlessness, and a worthy person is someone who stands up for da’as Torah and leads public opinion instead of being led by it. He does not subject his views to those of others. Such a person is worthy of protecting the entire public, because since he really leads the public his merit accrues to them. However, if he is not strong and relentless like a tree, but is rather subject to the influence of others and to public opinion, then even if he is a talmid chochom and a yerei shomayim he does not have the merit, and therefore the ability, to protect the public.
Furthermore, a tree bears fruit, and fruit symbolize the deeds of a person. This teaches us that in order for a talmid chochom to be able to save a town he must make an impression on it and bear “fruit”. He must disseminate Torah and good deeds. If he lives only for himself without influencing his fellow inhabitants, he is not capable of protecting the town in which he lives.
