But they are altogether brutish and foolish: the stock is a doctrine of vanities.
They are altogether - rather, all alike (Maurer).
Brutish - even the so-called "wise" men (Jeremiah 10:7) of the Gentiles are on a level with the brutes and "foolish," namely, because they connive at the popular idolatry (cf. Romans 1:21-28. Therefore, in Daniel and Revelation, the world-power is represented under a bestial form. Man divests himself of his true humanity, and sinks to the level of the brute, when he severs his connection with God (Psalms 115:8; Jonah 2:8).
The stock is a doctrine of vanities. The stock (put for the worship of all idols whatever, made out of a stock) speaks for itself, that the whole theory of idolatry is vanity (Isaiah 44:9-11, "They that make a graven image are all of them vanity, and their delectable things shall not profit; and they are their own witnesses: they see not, nor know, that they may be ashamed"). Castalio translates, 'the very wood itself confuting the vanity' (of the idol).
In Jeremiah 10:9, everything connected with idols is the result of human effort.