Albert Barnes Commentary Jeremiah 35:19

"therefore thus saith Jehovah of hosts, the God of Israel: Jonadab the son of Rechab shall not want a man to stand before me for ever." — Jeremiah 35:19 (ASV)

Travelers bear witness to the existence of a large tribe who represent themselves as the descendants of the Rechabites. The prediction was also literally fulfilled in the Rechabites being in some way incorporated into the tribe of Levi, whose office especially it was to stand before Yahweh (Deuteronomy 10:8).