John Calvin Commentary Lamentations 3:45

"Thou hast made us an off-scouring and refuse in the midst of the peoples." — Lamentations 3:45 (ASV)

They say here that they were exposed to reproach, so as to become, as it were, the sweepings of the world. Some render סחי, sachi, “refuse;” some by other words; and some “filth.” But the word properly means sweepings or scrapings, called by the Greeks περιψήματα.

Paul says that he and his associates were the offscouring of the world (περιψήματα) (1 Corinthians 4:13). He means that they were despised as offscourings or scrapings. The word is derived from sweeping. Whatever, then, is cleaned off by sweeping or scouring—that is, the filth of the house or the floor—is called סחי, sachi.

What the Prophet meant is not obscure; for he means that the degradation of the people was not hidden but open to all nations, as though God had erected a theater in Judea and there exhibited a remarkable and an unusual example of His vengeance. What he adds is to the same purpose.