He did not depend upon his own judgment in reading the character of his guests. By his tent a tree was planted, which spread its branches out over all who believed in God, and afforded them shade. But if idolaters went under the tree, the branches turned upward, and cast no shade upon the ground. Whenever Abraham saw this sign, he would at once set about the task of converting the worshippers of the false gods.
And as the tree made a distinction between the pious and the impious, so also between the clean and the unclean. Its shade was denied them as long as they refrained from taking the prescribed ritual bath in the spring that flowed out from its roots, the waters of which rose at once for those whose uncleanness was of a venial character and could be removed forthwith, while others had to wait seven days for the water to come up.
Accordingly, Abraham bade the three men lean against the trunk of the tree. Thus he would soon learn their worth or their unworthiness.