John Calvin Commentary Jeremiah 35:11

"But it came to pass, when Nebuchadrezzar king of Babylon came up into the land, that we said, Come, and let us go to Jerusalem for fear of the army of the Chaldeans, and for fear of the army of the Syrians; so we dwell at Jerusalem." — Jeremiah 35:11 (ASV)

Therefore, it appears that it was advantageous for the Rechabites to observe what their father had commanded them. If they had been tied to their possessions, they would have been driven into exile with the rest when the kingdom of Israel was destroyed. What happened to the ten tribes must also have happened to the Rechabites.

But as they had nothing of their own, they were freer to move elsewhere. Nor did they face the trial of leaving possessions, for they had none. We know that many are so tied to their own houses, fields, vineyards, and meadows, that they would rather be killed a hundred times than be torn away from them.

Then Jenadab wisely considered the benefit for his descendants when he ordered them to dwell in tents, for in this way they could gather all they had in one day, according to the known saying of Bias. Therefore, poverty was a great advantage to them. Their austerity of life was also a benefit, enabling them to dwell in Jerusalem without difficulty, as they had no need for many luxuries.

If they had been accustomed to wine and other delicacies, they might have debated whether it would have been better for them to die at once than to suffer hardship in a besieged city. Moreover, as they had lived frugally and had also been accustomed to an austere life, no anxiety prevented them from coming confidently to Jerusalem, for they thought that they could gain a meager and humble subsistence by their own labor.

So it now appears what Jenadab had in view when he forbade his descendants the use of wine as well as the possession of fields and vineyards, for he could then foresee what dreadful upheavals were near. It was therefore his purpose to train his descendants in this way, so that when difficulties came they might not succumb to the burden, but patiently bear hardship or any other inconvenience that would be intolerable to others when they remembered their former delicacies.

We they said, Come, and let us enter into Jerusalem from the face of both armies. Therefore, when the Israelites were detained by their fields and domestic possessions, the Rechabites went to Jerusalem and were thus freed from danger.