Musar do Rodzaju 18:9

Nowadays, when we all recite the appropriate benedictions, our Torah study can be classified as לשמה. In the final analysis, of course, only G–d knows if our Torah study is truly motivated by the proper thoughts; the matter is left to our hearts, it can never be demonstrated. The Torah frequently writes: ויראת מאלוקיך, "you shall fear the Lord;" such instructions refer to matters which cannot be proved except to G–d, for no man can look into our hearts. Neither do the ministering angels know what goes on in our hearts. They are only able to see what G–d has revealed to them. We know this from the Zohar's comment on Genesis 18,9 (Sullam edition Vayera 33) where the angels asked Abraham about Sarah's whereabouts. [Sarah's laughter which she did not articulate was something that G–d had revealed to these angels specifically then. Ed.] Tosafot in Shabbat 12 question how it is possible that the angels do not understand Aramaic seeing they can even see what goes on in our hearts. I have dealt with this apparent contradiction elsewhere; the overwhelming consensus among all our sages is that (normally) the ministering angels do not know what goes on in our hearts. Hence we have one version in which the explanation of Jeremiah 9,11 was sought from the prophets, the sages, and the ministering angels. They could not provide an answer since they did not know our thoughts and and therefore were unable to know if we study Torah לשמה or for ulterior motives. The Talmud therefore says that the meaning had to be explained by G–d Himself, since only He knows what goes on in our hearts. It follows that the passage in Nedarim mentioning that "the earth was lost" refers to the land of Israel.