25. The union of good and truth in others is provided for by the Lord by means of purification; and this is effected in two ways, one by temptations, and the other by fermentations. Spiritual temptations are nothing else than combats against evils and falsities which emanate from hell and make their influence felt. By these combats man is purified from evils and falsities, and good is united to truth in him, and truth to good. Spiritual fermentations are effected in many ways, both in the heavens and on the earth; but in the world it is not known what they are and how they are effected. Now there are evils together with falsities which, when introduced into societies, act like ferments put into meal and juice of the grape. By means of these, discordant things are separated and concordant things are united, and purity and clearness are the result. They are what are meant by these words of the Lord:
The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened. Matt. i. 33; Luke xiii. 21.