7906. 'No yeast shall be found in your houses' means no falsity whatever shall come near good. This is clear from the meaning of 'yeast' as falsity, dealt with below; and from the meaning of 'house' as good, dealt with in 3652, 3720, 4982, 7833-7835. The meaning of 'yeast' as falsity becomes clear from the places where yeast and anything made with yeast, and also where unleavened and anything made without yeast are mentioned, such as in Matthew,

Jesus said, Look out for and beware of the yeast of the Pharisees and Sadducees. Then the disciples understood that He had not said that they should beware of the yeast used in bread, but of the teaching of the Pharisees and Sadducees. Matthew 16:6, 11.

Here 'yeast' plainly stands for false teaching. Because 'yeast' meant falsity it was forbidden to sacrifice the blood of the sacrifice with anything made with yeast, Exodus 23:18; 34:25. For 'the blood of the sacrifice' meant holy truth, thus truth pure and free from all falsity, 4735, 6978, 7317, 7326, 7846, 7850. It was also laid down that the minchah offered on the altar should not be baked with yeast in it, Leviticus 6:15-17, and that cakes and wafers also should be made without yeast, Leviticus 7:11-13.

[2] To go further with what 'made with yeast' and 'not made with yeast' refer to, it should be recognized that the purification of truth from falsity cannot ever come about in a person without so called fermentation, that is, without the conflict of falsity with truth and of truth with falsity. But after the conflict has taken place and truth has triumphed, the falsity falls away like dregs and the truth emerges purified. It is like wine that becomes clear after fermentation as the dregs sink to the bottom. That fermentation or conflict takes place especially when a person's state undergoes a change, that is to say, when his actions begin to spring from the good of charity, and not as previously from the truth of faith. For a person's state is not yet made pure while his actions spring from the truth of faith, but they have been made pure when they spring from the good of charity, since they now spring from his will. Previously they sprang merely from his understanding.

[3] Spiritual conflicts or temptations are fermentations in the spiritual sense, for during them falsities wish to link themselves to truths, but the truths reject them, eventually sending them to the bottom so to speak and in that way becoming refined. This is the sense in which to understand what the Lord teaches about 'yeast' in Matthew,

The kingdom of heaven is like yeast, which a woman took and hid in three measures of flour, until the whole was fermented by it. Matthew 13:33.

'Flour' is truth from which good is derived. Also in Hosea,

They are all committing adultery, like an oven heated by a baker; the raiser ¹ ceases from kneading the dough until it has fermented. Hosea 7:4.

Since such conflicts, meant by 'fermentations', take place with a person in the state before he attains newness of life, as has been stated, it was also laid down that the new minchah, the bread of the wave-offering, that was to be brought at the feast of first fruits, should be baked with yeast; and that was to be the first fruits to Jehovah, Leviticus 23:16-17.

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4018. 'In front of the flocks; and they came on heat as they came to drink' means even to the point of an intense desire in the affection for truth that a joining [to the goods and truths within the natural] might be effected. This is clear from the meaning of 'coming on heat as they came to drink' as an intense desire. The meaning of 'being on heat' as an intense desire is self-evident; and for the meaning of 'coming to drink' as the affection for truth, see immediately above in 4017. The reason why 'in front of the flocks' means that a joining to the truths and goods within the natural might be effected is that this phrase implies seeing and consequent arousal of affection, for this is the manner in which spiritual things are joined to a person. What is more, every implantation of truth or good in a person, as well as every joining of them to him, is effected by means of affection. The truths and goods which a person has learned but for which he has no affection do indeed enter the memory, but they are lodged there as insecurely as a feather on top of a wall which is blown off by the slightest puff of wind.

[2] As regards the things that enter the memory the position is this: Those for which there is no affection pass into the unlit parts of the memory when they enter it, whereas those for which there is affection pass into the light there. Things present in that light are seen and appear clearly and distinctly when any matter of a similar nature is brought up, but not so the things lying around in the unlit parts. Such is the effect that affection belonging to love has. From this it may be seen that all implanting of truth and joining of it to good is effected through affection; and the greater that affection, the stronger the tie joining the two together.

[3] The intense desire of the affection is in this case inmost affection. But truths are not capable of being implanted and joined to good except by means of affections for truth and good, which affections well up from charity towards the neighbour and love to the Lord as their sources. But evils and falsities are implanted by means of affections for evil and falsity, and these affections well up from self-love and love of the world as their sources. This being so, and the subject at this point in the internal sense being the joining of good and truth within the natural man, mention is therefore made here and in what follows of the flock being on heat when they came to drink, by which such considerations are meant.