What is the meaning of "Lehodi'acha Koshet Imrei Emes"?
Rashi: This is why I wrote to you Shalishim, so you will understand from them. Koshet Imrei Emes is to answer sayings of Emes.
Malbim (20-21): There is a difference between Koshet and Emes. Emes is intrinsically true, even if no one knows the reason. The truth of Koshet is revealed and explained to all. My Meshalim will inform you of the Koshet and Emes of Imrei Emes. You will understand the reasons for the Emes that you accepted. Lehodi'acha corresponds to Mo'etzos; Lehashiv corresponds to Da'as.
Who is "Sholechecha"?
Rashi: The one who asks you for a ruling.
R. Yonah (10:26): The one who sent him on a mission. Refer to 10:26:3:1.
Malbim: It is others. Since you will understand the proofs of Da'as, you will be able to help others get a clear knowledge of the reasons for Chachmah.
