Adam Clarke on Isaiah 54:1

Sing, O barren, thou that didst not bear "Shout for joy, O thou barren, that didst not bear" - The Church of God under the Old Testament, confined within the narrow bounds of the Jewish nation, and still more so in respect of the very small number of true believers, and which sometimes seemed to be deserted of God her husband, is the barren woman, that did not bear, and was desolate. She is exhorted to rejoice, and to express her joy in the strongest manner, on the reconciliation of her husband, (see Isa 54:6), and on the accession of the Gentiles to her family. The converted Gentiles are all along considered by the prophet as a new accession of adopted children, admitted into the original Church of God, and united with it. See Isa 49:20, Isa 49:21.