249. 13. Of these external reasons for coldness, a fourth is an absence of focus on any pursuit or business, resulting in promiscuous lust. Human beings were created to be useful, because useful service is the containing vessel of goodness and truth, and a marriage of good and truth is the origin both of creation and also of conjugial love (as we showed in its own chapter). 1
By pursuit or business we mean any effort to be useful. When as a result a person is engaged in some pursuit or business or other useful activity, his mind is fenced around and circumscribed as though with a circle, within whose bounds it is progressively ordered into truly human form. Then, from this vantage point, as though looking out from its house, it sees various impure passions lurking outside, and from the sanity of its reason within, banishes them, thus banishing as well the wild insanities of licentious lust. Because of this, conjugial warmth lasts better and longer in such people than it does in others.
 The contrary happens in the case of people who surrender themselves to laziness and sloth. Their mind is not fenced around or set within bounds; a person like that consequently throws open the whole of it and lets in every sort of nonsense and foolishness which flows in from the world and the body and draws him into a love of them. It is apparent that conjugial love is also then cast out and banished. For laziness and sloth dull the mind and numb the body, and the whole person becomes unresponsive to any vitalizing love - especially conjugial love, from which, as from a fountain, spring active and energetic states of life.
In such people, however, the coldness they feel in marriage is different from the same coldness in others. It is indeed an absence and loss of conjugial love, but from a failure of ability.