Charles Ellicott Commentary Jeremiah 6:10

"To whom shall I speak and testify, that they may hear? behold, their ear is uncircumcised, and they cannot hearken: behold, the word of Jehovah is become unto them a reproach; they have no delight in it." — Jeremiah 6:10 (ASV)

To whom shall I speak ...?—The prophet, who now speaks in his own name, has heard the message from the Lord of Hosts; but what use is it? Who will listen? As elsewhere the lips (Exodus 6:30) and the heart (Leviticus 26:41; Ezekiel 44:7), so here the ear of Israel was uncircumcised, as if it had never been brought into covenant with Jehovah or consecrated to His service.

A reproach. — i.e., the object of their scorn.