This point is made so that the reason may grasp the necessity, usefulness and truth of the proposition that conjugial love, where it is not genuine, should still be professed and made to look as if it were. It would be different if marriages entered into were not a promise lasting until the end of one's life, but something which could be ended at will. This was the situation of the Israelite people, who claimed for themselves the freedom to divorce wives for any reason whatsoever. This is plain from this passage in Matthew:

Some Pharisees came and said to Jesus, Is it permissible for a person to divorce his wife for any reason? And when Jesus replied that it was not permissible to divorce one's wife and marry another, except for unchaste conduct, they retorted that Moses had commanded them to give notice of repudiation and to divorce. And the disciples said, If this is a person's situation in respect of his wife, it is preferable not to marry. Matt. 19:3-10.

[2] Since therefore the marriage contract is for life, it follows that couples are bound to keep up the appearance of love and friendship. The need for marriages entered into to be maintained until the end of life in the world arises from God's law, and this being so, it is prescribed by the law of reason too, and so is a matter of civil law. It is God's law that it is not permissible to divorce a wife and marry another, except for unchaste conduct, as was shown just above. It is the law of reason, because this is founded upon the spiritual law, since God's law is one with the law of reason. These two together, or rather the law of reason inspired by God's law, [give rise to the civil law. Today]* numerous examples are to be seen of aberrations, the destruction of communities, and the dissolution of marriage before death or the divorce of wives at the husband's whim. These aberrations and the destruction of communities can be seen discussed at some length in the account of the debate on the origin of conjugial love by the representatives of the nine kingdoms (103-115). There is thus no need to give additional reasons. These reasons, however, do not prevent separation being permissible for special causes (on these see 252-254 above); and also having a concubine (which is discussed in Part Two [Chapter XX]). * The sentence appears to be incomplete in the original.