5 Still, the purpose We have set before Us is not to recount, in detail, benefits of this kind; Our wish is rather to speak about that family union of which marriage is the beginning and the foundation. The true origin of marriage, venerable brothers, is well known to all. Though revilers of the Christian faith refuse to acknowledge the never-interrupted doctrine of the Church on this subject, and have long striven to destroy the testimony of all nations and of all times, they have nevertheless failed not only to quench the powerful light of truth, but even to lessen it. 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. God thus, in His most far-reaching foresight, decreed that this husband and wife should be the natural beginning of the human race, from whom it might be propagated and preserved by an unfailing fruitfulness throughout all futurity of time. And this union of man and woman, that it might answer more fittingly to the infinite wise counsels of God, even from the beginning manifested chiefly two most excellent properties - deeply sealed, as it were, and signed upon it-namely, unity and perpetuity. From the Gospel we see clearly that this doctrine was declared and openly confirmed by the divine authority of Jesus Christ. He bore witness to the Jews and to His Apostles that marriage, from its institution, should exist between two only, that is, between one man and one woman; that of two they are made, so to say, one flesh; and that the marriage bond is by the will of God so closely and strongly made fast that no man may dissolve it or render it asunder. "For this cause shall a man leave father and mother, and shall cleave to his wife, and they two shall be in one flesh. Therefore now they are not two, but one flesh. What, therefore, God bath joined together, let no man put asunder."(2)
Source: Arcanum Divinae (Vatican.va)