24. The union of good and truth is provided for by the Lord by means of related sequence; for the quality of a good is known only by its relation to what is less good, and by the opposition it meets from evil. From this relation comes the power to perceive and to feel, since from this comes the quality of these powers; for thus everything that is pleasant is perceived and felt from what is less pleasant and by means of what is unpleasant; everything beautiful from what is less beautiful, and by means of the ugly; and likewise every good, which is of love, from what is less good and by means of evil; and every truth, which is of wisdom, from what is less true and by means of falsity.
There must be variation in everything, from its greatest to its least; and as there is also variation in its opposite from its least to its greatest, with equilibrium between them, then there is relation in sequence on both sides according to degrees; and the perception and sensation of the thing increase or diminish. It should be known, however, that an opposite destroys as well as exalts perceptions and sensations: it destroys when it mingles them with itself and exalts when it does not. For this reason the Lord most carefully separates good and evil in man lest they should be mingled, just as He separates heaven and hell.