Why did the Law of Moses allow divorce?

St. Augustine says, “For He who gave the commandment that a writing of divorcement should be given, did not give the commandment that a wife should be put away; but whosoever shall put away, says He, let him give her a writing of divorcement, in order that the thought of such a writing might moderate the rash anger of him who was getting rid of his wife. And, therefore, He who sought to interpose a delay in putting away, indicated as far as He could to hard-hearted men that He did not wish separation. And accordingly the Lord Himself in another passage, when a question was asked Him as to this matter, gave this reply:

1765 St. Jacob of Sarug, Homily 205 on celibacy, adultery and the marriage of righteousness .

1766 St. Athenagoras, A Plea for the Christians 33 (ANF 2:146).

1767 See St. Augustine, Sermons on Selected Lessons of the New Testament 1.22 (NPNF I/6:253).

1768 Cf. St. Ignatius of Antioch, Epistle to Polycarp 5 (ANF 1:95).

1769 St. Clement of Alexandria, Stromateis, Books 1–3 3.12.79.5 (FOTC 85:305).

1770 Origen, Commentary on the Epistle to the Romans , Books 6–10 9.1.7 (FOTC 104:194).

1771 Origen, Commentary on 1 Corinthians 3.39.51–52.

‘Moses, because of the hardness of your hearts, permitted you to divorce your wives’ (Matt. 19:8). For however hard-hearted a man may be who wishes to put away his wife, when he reflects that, on a writing of divorcement being given her, she could then without risk marry another, he would be easily appeased. Our Lord, therefore, in order to confirm that principle, that a wife should not lightly be put away, made the single exception of fornication; but enjoins that all other annoyances, if any such should happen to spring up, be borne with fortitude for the sake of marital faithfulness and for the sake of chastity; and he also calls that man an adulterer who should marry her that has been divorced by her husband.”¹⁷⁷²