Jeremiah 2:5

Has Israel had any excuse for their disloyalty to Me? None.

have walked after vanity -vanity" (lit. a breath) is here used in the same sense as in 1 Kings 16:13. Jehovah and His prophets regarded idols simply as unsubstantial, unreal things. Hence -vanity" (i.e. idols) expresses their view. So in 1 Corinthians 8:4. Cp. Jeremiah 2:8; Jeremiah 2:11, Jer 16:19; 1 Samuel 12:21; Isaiah 44:9 f. Ch. Jeremiah 10:10 contrasts God as "the true God," "the living God"; while the notions of that which is unreal and that which is positively injurious are combined in Jeremiah 16:19.

and are become vain have their characters assimilated to the objects which they serve. Cp. Romans 1:21 f., they "became vain in their reasonings … they became fools."