Albert Barnes Commentary Jeremiah 3:23

"Truly in vain is [the help that is looked for] from the hills, the tumult on the mountains: truly in Jehovah our God is the salvation of Israel." — Jeremiah 3:23 (ASV)

Rather, surely in vain from the hills is the revelry of the mountains. The penitents contrast in it the uselessness of idol-worship with the salvation which Yahweh gives to His people.