Charles Ellicott Commentary Isaiah 51:11

"And the ransomed of Jehovah shall return, and come with singing unto Zion; and everlasting joy shall be upon their heads: they shall obtain gladness and joy; [and] sorrow and sighing shall flee away." — Isaiah 51:11 (ASV)

Therefore the redeemed. —Noteworthy as being either a quotation by Isaiah from himself (Isaiah 35:10), or by the unknown writer of Isaiah from the earlier prophet. The assumption that it is an interpolation by a copyist rests on no adequate ground.