Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Jer 35:1-11) The obedience of the Rechabites.
(Jer 35:12-19) The Jews' disobedience to the Lord.
Jonadab was famous for wisdom and piety. He lived nearly 300 years before, Kg2 10:15. Jonadab charged his posterity not to drink wine. He also appointed them to dwell in tents, or movable dwelling: this would teach them not to think of settling any where in this world. To keep low, would be the way to continue long in the land where they were strangers. Humility and contentment are always the best policy, and men's surest protection. Also, that they might not run into unlawful pleasures, they were to deny themselves even lawful delights. The consideration that we are strangers and pilgrims should oblige us to abstain from all fleshly lusts. Let them have little to lose, and then losing times would be the less dreadful: let them set loose to what they had, and then they might with less pain be stript of it. Those are in the best frame to meet sufferings who live a life of self-denial, and who despise the vanities of the world. Jonadab's posterity observed these rules strictly, only using proper means for their safety in a time of general suffering.
The trial of the Rechabites' constancy was for a sign; it made the disobedience of the Jews to God the more marked. The Rechabites were obedient to one who was but a man like themselves, and Jonadab never did for his seed what God has done for his people. Mercy is promised to the Rechabites. We are not told respecting the performance of this promise; but doubtless it was performed, and travellers say the Rechabites may be found a separate people to this day. Let us follow the counsels of our pious forefathers, and we shall find good in so doing.