Commentaries:
"Let them" (verse 11), meaning the inhabitants of Selah and certainly, in a smaller sense, those previously mentioned, but the focus is on those in Selah.
John W. Ritenbaugh
A Place of Safety? (Part 2)
This place has all of the benchmarks of the Place of Safety: wilderness, a rock, Selah, Kedar. Where is Kedar? It is in what is today northwest Saudi Arabia, and it is the general name of the area in which Selah (Petra) was located.
Consider this: Today, that area contains nothing more than Bedouins passing through. God commands the inhabitants—those who live there—to sing praises to Him. Does it seem logical that at the end time when God goes forth, that the Bedouins would be singing praises to God? No, someone else inhabits Selah, who will glorify and sing praises to God. It is those who are being sheltered there when the Lord goes forth like a mighty warrior.
John W. Ritenbaugh
A Place of Safety? (Part 2)