Isaiah 21 · a question people ask
Does the chapter say why the glory of Kedar will fail?
No. It says when, "Within a year" (21:16), and who has spoken: "for the LORD, the God of Israel, has spoken it" (21:17). The burden on Arabia names no sin of the Dedanites, of Tema or of Kedar, and it doesn't say whose swords the fugitives fled (21:15). These notes read the chapter as it stands, add no history of these peoples from outside the Bible, work out no date from "Within a year", and apply nothing in the chapter to any people or place today.
The verses
“The burden on Arabia. You will lodge in the thickets in Arabia, you caravans of Dedanites. They brought water to him who was thirsty. The inhabitants of the land of Tema met the fugitives with their bread. For they fled away from the swords, from the drawn sword, from the bent bow, and from the heat of battle. For the Lord said to me, “Within a year, as a worker bound by contract would count it, all the glory of Kedar will fail, and the residue of the number of the archers, the mighty men of the children of Kedar, will be few; for the LORD, the God of Israel, has spoken it.””