Isaias 54:3

In Isaiah: “Rejoice, thou barren, that barest not; and break forth and cry, thou that travailest not: because many more are the children of the desolate one than of her who hath an husband. For the Lord hath said, Enlarge the place of thy tabernacle, and of thy curtains, and fasten them: spare not, make long thy measures, and strengthen thy stakes: stretch forth yet to thy right hand and to thy left hand; and thy seed shall possess the nations, and shall inhabit the deserted cities. Fear not; because thou shalt overcome: nor be afraid because thou art cursed; for thou shalt forget thy eternal confusion.” Thus also to Abraham, when his former son was born of a bond-woman, Sarah remained long barren; and late in old age bare her son Isaac, of promise, who was the type of Christ. …

But let us now hear what follows about the Church. He says, “Rejoice, O barren, thou that barest not; break forth and cry, thou that didst not travail with child: for many more are the children of the desolate than of her that has an husband.” But these must suffice; and some things in them ought to be expounded; yet I think those parts sufficient which are so plain that even enemies must be compelled against their will to understand them.

10. “And Thou, Lord God of virtues, God of Israel.” Thou God of Israel, that art thought to be but God of one nation, which worshippeth Thee, when all nations worship idols, Thou God of Israel, “Give heed unto the visiting all nations.” Fulfilled be that prophecy wherein Isaiah in Thy person speaketh to Thy Church, Thy holy City, that barren one of whom many more are the sons of Her forsaken than of her that hath a husband. To Her indeed hath been said, “Rejoice, thou barren, that bearest not,” etc., more than of the Jewish nation which hath a Husband, which hath received the Law, more than of that nation which had a visible king. …