That the Church which before had been barren should have more children from among the Gentiles than what the synagogue had had before
In Isaiah: “Rejoice, you barren, that bar-est not; and break forth and cry, you that travailest not: because many more are the children of the desolate one than of her who has an husband. For the Lord has said, Enlarge the place of your tabernacle, and of your curtains, and fasten them: spare not, make long your measures, and strengthen your stakes: stretch forth yet to your right hand and to your left hand; and your seed shall possess the nations, and shall inhabit the deserted cities.
Fear not; because you shall overcome: nor be afraid because you are cursed; for you shall forget your 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. Thus also Jacob received two wives: the eider Leah, with weak eyes, a type of the synagogue; the younger the beautiful Rachel, a type of the Church, who also remained long barren, and afterwards brought forth Joseph, who also was himself a type of Christ.
And in the first of Kings it is said that Elkanah had two wives: Peninnah, with her sons; and Hannah, barren, from whom is born Samuel, not according to the order of generation, but according to the mercy and promise of God, when she had prayed in the temple; and Samuel being born, was a type of Christ. Also in the first book of Kings: “The barren has borne seven and she that had many children has grown weak.” But the seven children are the seven churches. Whence also Paul wrote to seven churches; and the Apocalypse sets forth seven churches, that the number seven may be preserved; as the seven days in which God made the world; as the seven angels who stand and go in and out before the face of God, as Raphael the angel says in Tobit; and the sevenfold lamp in the tabernacle of witness; and the seven eyes of God, which keep watch over the world; and the stone with seven eyes, as Zechariah says; and the seven spirits; and the seven candlesticks in the Apocalypse; and the seven pillars upon which Wisdom has built her house in Solomon.
Source: The Treatises of Cyprian (New Advent)