506. And the third part of the trees was burnt up, signifies that the perceptions and knowledges of truth and good were destroyed by cupidities arising from evil loves. This is evident from the signification of "a third part," when predicated of truths, as meaning all (of which presently); also from the signification of "trees," as being the interiors of man that belong to his mind (of which above, n. 109), and thus the perceptions of truths and goods, and the knowledges of them (see above, n. 420); also from the signification of "to be burnt up," as being to be destroyed by cupidities arising from evil loves, of which just above (n. 504), where it was shown that these cupidities are signified by "fire," therefore "to be burnt up" means to be destroyed by these.  "The third part" signifies all, and thus "the third part of the trees" signifies every perception of truths and goods, and thence every knowledge of them, because the number "three" signifies fullness, the whole, and all, and is predicated of truths; so "the third part" has the like meaning, for "a third" means the same as "three;" moreover, numbers multiplied into themselves and divided by themselves have a similar signification as the integral numbers from which they are derived (see above, n. 430). That "the third part" signifies all and is predicated of truths see also above (n. 384). "The third part" has a similar signification in the following passages:
The third part of the sea became blood (verse 8);
The third part of the creatures that were in the sea died (verse 9);
A burning star fell upon the third part of the rivers (verse 10);
The third part of the waters became wormwood (verse 11);
The third part of the sun was smitten, and the third part of the moon, and the third part of the stars (verse 12; likewise 9:15, 18; 12:4).  This describes how all perception of truth and good, and thence the knowledge of them, were first destroyed by the loves of self and the world and the cupidities and pleasures arising therefrom. The perception and knowledge of spiritual truth and good are destroyed by these loves and the cupidities arising therefrom, because these loves are the corporeal and merely natural loves into which man is born and unless these are subdued and ruled by spiritual loves, which are out of heaven from the Lord, they extinguish every perception and thence every knowledge of the truths and goods of heaven and the church; for these loves regarded in themselves are diametrically opposite to the spiritual loves. From this it can be seen that when the church lapses it comes first from an internal spiritual state into a natural state, that consists of loving self and the world above all things; thence then it is in thick darkness in respect to all things of heaven and the church, however much light it may have in respect to the things of the world.  When the perception of spiritual truths and goods perishes, the knowledge of them also perishes, for although man knows them and speaks of them from the Word or from doctrine, still he does not know them when he does not perceive them. The perception of a thing makes the knowledge of it. Knowledge without perception is not living, but dead, and is a knowledge of the mere sense of the words, and not of the thing itself. Such are the knowledges of truth and good from the Word and from the doctrine of the church that those have with whom the loves of self and the world are dominant; however skilled such may be in cleverly and artfully speaking and preaching about them, yet they are mere shells, which seem before the vulgar to have kernels within, and yet they are empty.