Pope Leo XIII began Arcanum by recalling the history of marriage, established in the Old Testament when God created man and woman: We record what is to all known, and cannot be doubted by any, that God, on the sixth day of creation, having made man from the slime of the earth, and having breathed into his face the breath of life, gave him a companion, whom He miraculously took from the side of Adam when he was locked in sleep.

Polygamy and divorce both became accepted practice such as men being allowed to violate their vows by having sexual relations outside of marriage.

[6] That the judgment of the Council of Jerusalem reprobated licentious and free love, we all know; as also that the incestuous Corinthian was condemned by the authority of blessed Paul.

The placing of marriage under the state as just another civil, contractual institution appeared to be a part of the on-going secular movement by the Freemasons and socialists of Leo's time.

[12]  In spite of that state's interest in marriage, marriage had a spiritual element and Leo saw that many of his predecessors had to stand up to the princes and emperors of their times who tried to relax the bonds of marriage: […] the decrees of Nicholas I against Lothair; of Urban II and Paschal II against Philip I of France; of Celestine III and Innocent III against Alphonsus of Leon and Philip II of France; of Clement VII and Paul III against Henry VIII; and, lastly, of Pius VII, that holy and courageous pontiff, against Napoleon I, at the height of his prosperity and in the fullness of his power.

[14] Summary of Arcanum from The Catholic Encyclopedia[15] Arcanum taught that since family life is the germ of society, and marriage is the basis of family life, the healthy condition of civil no less than of religious society depends on the inviolability of the marriage contract.

But human weakness and willfulness began to throw off the bridle of Christian discipline in family life; civil rulers began to disown the authority of the church over the marriage tie; and rationalism sought to sustain them by establishing the principle that the marriage contract is not a sacrament at all, or at least that the natural contract and the sacrament are separable and distinct things.

The encyclical points to the consequences of that departure in the breaking up of family life, and its evil effects on society at large.