Therefore — This verse contains an answer to the prophet's prayer. I did these great things, and I will do the like again. Joy — Like a crown of glory.
Related Commentaries of Isaiah 51:11
Isaiah 51:11
11 Therefore the redeemed of the LORD shall return, and come with singing unto Zion; and everlasting joy shall be upon their head: they shall obtain gladness and joy; and sorrow and mourning shall flee away.