Of these two, that, which be set first, pertains unto command, against which it is not lawful to do. For it is not lawful to put away a wife, save because of fornication,  as the Lord Himself saith in the Gospel. But that, which he added, "Thou art loosed from a wife, seek not a wife," is a sentence of counsel, not of command; therefore it is lawful to do, but it is better not to do. Lastly, he added straightway, "Both if thou shalt have taken a wife, thou hast not sinned; and, if a virgin shall have been married, she sinneth not."  But, after that former saying of his, "Thou art bound to a wife, seek not loosening," he added not, did he, "And if thou shalt have loosed, thou hast not sinned?" For he had already said above, "But to these, who are in marriage, I command, not I, but the Lord, that the wife depart not from her husband: but, if she shall have departed, that she remain unmarried, or be reconciled unto her own husband;" for it may come to pass that she depart, not through any fault of her own, but of her husband. Then he saith, "And let not the man put away his wife," which, nevertheless, he set down of command of the Lord: nor did he then add, And, if he shall have put her away, he sinneth not. For this is a command, not to obey which is sin: not a counsel, which if you shall be unwilling to use, you will obtain less good, not do any ill. On this account, after he had said, "Thou art loosed from a wife, seek not a wife;" because he was not giving command, in order that there be not evil done, but was giving counsel, in order that there be done what is better: straightway he added, "Both, if thou shall have taken a wife, thou hast not sinned; and, if a virgin shall have been married, she sinneth not."
 1 Cor. vii.10, 11