Tertullian, On Monogamy 10

I see we are now being summoned to the Apostle. To make his mind more easily understood, it must be driven home all the more urgently that a woman is bound to her dead husband and cannot take another. Consider: divorce arises from discord, or discord causes it; but death comes by the law of God, not by a man's offense. And death is a debt owed by all, even the unmarried. So if a woman divorced because of discord, anger, hatred, and their causes — injury, insult, or any grievance — is separated in soul and body, she remains bound to her enemy, I will not say her husband; how much more, then, is the woman bound who, neither by her own fault nor her husband's, but by the outcome of the Lord's law, was not severed from marriage but left behind? She will belong to him even in death, the very man to whom she owes concord even now that he is dead. She never heard a repudiation from him; she was never turned away. No certificate of divorce was written for her; she remains with him. She did not want to lose him; she keeps him. She holds the freedom of her mind, which presents to a man everything he lacks as an imaginary fruit. (1 Corinthians 7)

I put the question to the woman herself: Tell me, sister, did you send your husband ahead in peace? What will she answer? Or in discord? Then she is bound to him all the more, because she has a case with him before God. The one who is held back does not depart — but in peace. Therefore she must persevere in that bond with him, since she cannot repudiate him now — not even if she were to marry, had she been able to repudiate him. For indeed she prays for his soul, asks refreshment for him in the meantime, and a share in the first resurrection, and she makes offerings on the annual anniversaries of his death. If she does not do these things, she has truly repudiated him, as far as it lies in her power; and this is all the more unjust, because she could not do it, precisely because she could not; and all the more unworthy, because it is now more unworthy, if she did not deserve it. Or do we suppose we become nothing after death, following some Epicurean rather than Christ? But if we believe the resurrection of the dead, we will surely be held to account, together with those with whom we will rise, to render an account of each other. (1 Corinthians 7)

Even if in that age they neither marry nor are given in marriage, but are like angels, that does not mean we will not be held to our deceased spouses, simply because marriage will not be restored. On the contrary, we will be held all the more, because we are destined for a better state: to rise into a spiritual fellowship, recognizing both ourselves and our own. How else will we sing thanks to God for eternity, if the sense and memory of this debt do not remain in us? If we are reformed in substance, not in conscience? Therefore, when we are with God, we will be together — while all of us, with God, are one (though rewards vary, though there are many dwellings with the same Father), having worked for the same wage, namely eternal life, in which God will no more separate those He has joined than He forbids separation in this lesser life. (1 Corinthians 7)

Since this is so, how will she be free for another man, when she is occupied with her own even in the future? We address both sexes, though the speech is directed to one; for a single discipline governs both. Will she have one man in spirit and another in flesh? That would be adultery — the conscience of one woman divided between two men. If the first is separated from the flesh but remains in the heart, there — where even a thought without bodily union perfects adultery from desire, and marriage from will — he is still a husband, possessing that by which he was made, namely the mind. If another dwells in that mind, it is a crime. Yet he is not excluded, if he has departed from the lower commerce of the flesh. The husband is more honored when he has been made purer. (1 Corinthians 7)