John Gills Exposition of the Bible Commentary

Verse 4 (Jeremiah 9:4)

Take ye heed everyone of his neighbour ,.... Take care of being imposed upon by them, since they are so given to lying and deceit; be not too credulous, or too easily believe what is said; or keep yourselves from them; have no company or conversation with them, since evil communications corrupt good manners:

and trust ye not in any brother ; whether by blood or by marriage, or by religion, believe not his words; trust him not, neither with your money, nor with your mind; commit not your secrets to him, place no confidence in him; a people must be very corrupt indeed when this is the case: or, "trust ye not in every brother" F18 ועל כל אח אל תבטחו "et omni fratri ne fidatis", Paganinus. ; some may be trusted, but not all though the following clause seems to contradict this,

for every brother will utterly supplant ; or, in supplanting supplant F19 עקוב יעקב "supplantanto supplantat", Schmidt. ; play the Jacob, do as he did by his brother, who supplanted him twice; first got the birthright from him, and then the blessing; which was presignified by taking his brother by the heel in the womb, from whence he had his name; and the same word is here used, which signifies a secret, clandestine, and insidious way of circumventing another;

and every neighbour will walk with slanders ; go about spreading lies and calumnies, as worshippers, backbiters, and tale bearers do. The word דכיל is used for a "merchant"; and because such persons went from place to place with their goods, and made use often times of fraudulent practices to deceive people, it is applied to one that is guilty of slander and calumny; Song of Solomon 3:8 .

- John Gills Exposition of the Bible Commentary