Charles Ellicott Commentary Amos 5:3

"For thus saith the Lord Jehovah: The city that went forth a thousand shall have a hundred left, and that which went forth a hundred shall have ten left, to the house of Israel." — Amos 5:3 (ASV)

Shall leave an hundred.— That is, shall have an hundred only as a remnant of the thousand who went forth to war. The great cities were to be decimated in the coming struggle with Assyria.