GEN832 We see how characteristic it is for the pious to express concern even regarding a mitzvah that has been fulfilled, saying, “Perhaps, Heaven forbid, something objectionable is intermingled in it.”  As for Abraham, after he had gone to the assistance of his nephew, Lot, who was in captivity, he became freighted and said that maybe his deeds were not completely pure.  This [derives] from what they of blessed memory explained Genesis Rabbah 44:4 about [this verse].  “Rabbi Levi said: Because Abraham became frightened, saying: ‘Among all the people that I have killed, might there not have been one righteous person or one God-fearing person?  [See also, 32:8 AMJV 62-3] Therefore he was told, ‘Abram, do not be afraid.’” In the Tanna D’Vei Eliyahu it says Eliyahu Rabbah 25: “Abram, do not be afraid’ [teaches us that] one only says ‘Do not be afraid’ to one who truly fears Heaven.  This is the true fear about which they said Berachot 33b: “The only thing the Holy One blessed be He has in His world is a storehouse that contains the fear of heaven.”  Only Moshe was able to attain it easily because of his great attachment to the Blessed One’s name.  For others, corporeality is unquestionably a great deterrent.  Nonetheless, every pious person should strive to attain as much as he is capable of attaining; and it says Psalms 34:10: “Fear the Eternal – you, His holy ones.”  PATH 172-3