Musar for Bava Batra 29:14

Likewise our sages, of blessed memory, expounded (Bava Batra 15a): "'is there a tree there?' (Bamidbar 13:20) - is there a righteous person who shields the generation like a tree".

Joshua and Caleb countered that whatever deity had protected the people of Canaan thus far had already departed from them, i.e. סר צלם מעליהם (14,9), and they had no longer any merits which would act as protection for them. The measure of guilt of the Emorite was by now such that it no longer could be a hindrance to Israel. The expression סר צלם, may be interpreted according to the Zohar on Genesis 18,4: "and recline under the tree." The significance of that tree was that Abraham could tell by it who was truly loyal to G–d, and who cleaved to idol worship. The tree would extend its branches towards those who believed in G–d and would envelop them in its shade. The same branches would withdraw when a person worshiping idols sat under it. Abraham would notice this and begin to engage such a person in a religious dialogue, pointing out the futility of worshiping idols. He would not move from there until he had converted the person in question. Similarly the tree would welcome those who were ritually pure, while rejecting those who were not. There was a well underneath that tree. The waters in the well would rise towards a person in need of purification. As soon as Abraham noticed, he would purify them by ritually pure water. What Moses had commanded the spies about investigating "a tree" (13,20), referred to the tradition mentioned in the Zohar. He wanted to find out how that tree would react when the spies were under it, if it would offer its shade, i.e. a sign that the spies were sincere, if it did not, it would signal the sinful motives of these people.