Albert Barnes Commentary Jeremiah 18:15

"For my people have forgotten me, they have burned incense to false [gods]; and they have been made to stumble in their ways, in the ancient paths, to walk in bypaths, in a way not cast up;" — Jeremiah 18:15 (ASV)

Because - “For.” Jeremiah returns to, and continues the words of, (Jeremiah 18:13).

Vanity - A word meaning “falsehood,” which signifies that the worship of idols is not merely useless but injurious.

They have caused them to stumble - Judah’s prophets and priests were those who made her err (Jeremiah 5:31). The idols were of themselves powerless for good or evil.

In their ways ... - Or, in their ways, the everlasting paths, to walk in byways, in a road not cast up.

“The paths of eternity” carry back the mind not to the immediate but to the distant past, and suggest the good old ways in which the patriarchs used to walk.

The “road cast up” means one raised sufficiently to keep it out of the reach of floods, etc.