It is uncertain whether father here signifies their immediate parent, or (which is more probable) their progenitor; it is most likely it referreth to that Jonadab of whom we read 2 Kings 10:15, who was the father (that is, the progenitor) of this family of the Rechabites, at three hundred years distance. The reason why he left his posterity this charge is uncertain, probably to warn them against the luxury which he saw began to abound in Israel, and being desirous that they should inure themselves to a more hard and laborious life; being originally Kenites, and used to husbandry, and keeping of sheep and other cattle, he desired they should live according to their quality.
Related Commentaries of Jeremiah 35:6
Jeremiah 35:6
6 But they said, We will drink no wine: for Jonadab the son of Rechab our father commanded us, saying, Ye shall drink no wine, neither ye, nor your sons for ever: