MeAm Lo'ez

54:1  The Community of Yisrael which had been taunted as being "barren" compared to the nations, shall again become a multitude.  She whose Land had been desolate compared to the nations', shall once again live in her Land.  So Yeshayahu now calls in G-d's Name to his people to rejoice over their future rebirth.  Rejoice that your children born in your "desertion" by G-d are more in quality than those born in your "marriage" to Him.  For those born in your marriage rebelled out of plenty, wheras those born in desertion turned to G-d out of want.  So break out in song and rejoice, for G-d finds your voice pleasant to hear - it expresses your purified souls.