5 I ask, then, what is the meaning of men's obstinate determination to shut their eyes and to refuse to look on what is as clear as day? I have said that there are diversities of gifts in the Church, and that virginity is one gift and wedlock another. And shortly after I have used the words: “I allow marriage also to be a gift of God, but there is a great difference between gift and gift.” Can it be said that I condemn that which in the clearest terms I declare to be the gift of God?
Moreover, if Joseph is taken as a type of the Lord, his coat of many colors is a type of virgins and widows, celibates and wedded. Can any one who has any part in Christ's tunic be regarded as an alien? Have we not spoken of the very queen herself— that is, the Church of the Saviour— as wearing a vesture of gold wrought about with various colors? Moreover, when I came to discuss marriage in connection with the following verses, I still adhered to the same view. “This passage,” I said, “has indeed no relation to the present controversy; for, following the decision of the Lord, the apostle teaches that a wife must not be put away saving for fornication, and that, if she has been put away, she cannot during the lifetime of her husband marry another man, or, at any rate, that she ought, if possible, to be reconciled to her husband.
In another verse he speaks to the same effect: 'The wife is bound...as long as her husband lives; but if her husband be dead, she is loosed from the law of her husband; she is at liberty to be married to whom she will; only in the Lord,' that is to a Christian. Thus the apostle, while he allows a second or a third marriage in the Lord, forbids even a first with a heathen.”
Source: Letters (New Advent)