Serpents represent what we know from our bodily senses, and the reasoning based on our senses. Since the people of the Most Ancient Church had become more external, they were susceptible to the lure of trusting their senses more than they trusted the leading of the Lord. That was particularly true for the sense of self the people had been given, which is represented by the woman. Eating of the trees in the garden represented taking in desires for good and true ideas from the knowledge granted them by the Lord.

So here, for the first time, we see people, from their own senses, actually questioning the Lord. From their senses they wished to explore the knowledge represented by fruit of the garden, but wondered why they were denied the tree of knowledge.

(参照: Arcana Coelestia 194, 195, 196, 197)

579. Verse 18. By these three was the third part of men killed, by the fire, and by the smoke, and by the brimstone, going out of their mouths, signifies that all the understanding of truth, and the spiritual life therefrom, were extinguished by them. This is evident from the signification of "the third part of men," as being all intelligence, or the understanding of truth, and as spiritual life is from this, that also is involved; from the signification of "to be killed," as being to be extinguished, for when the understanding of truth is extinguished man is spiritually killed see above, n. 315; the "third part," in reference to truths, means all (See above, n. 506); and "man" means the understanding of truth and the perception of good (n. 280, 546); also from the signification of "fire, smoke, and brimstone going out of their mouths," as being the thoughts and reasonings therefrom springing from the love of evil, from the love of falsity, and from the lust of destroying truths and goods by the falsities of evil (See above, n. 578). From this the signification of these words can be seen. This is said of the horses seen in vision, namely, that "out of their mouths went out fire, smoke, and brimstone;" and as the "horses" seen in vision signify the falsifications of the Word by reasonings from fallacies, it is evident that "fire, smoke, and brimstone," signify the things that cause falsification, which are the loves of evil and falsity, and the lusts for destroying the truths and goods of the church. This is effected by the thoughts and by reasonings from fallacies about the sense and understanding of the Word. For when a man thinks from mere fallacies he thinks solely from such things as stand forth at first sight in the sense of the letter, and not from any interior literal sense; consequently he forms the most gross and harsh ideas respecting every doctrine he derives from the Word, as that God is angry, that He punishes, casts men into hell, tempts them, that He repents, and many like things; moreover, he thinks corporeally and materially, and not at all spiritually, about everything he reads in the Word; for this reason his thought is merely sensual, and when it is merely sensual it is solely from the love of self and of the world, and when it is from these it is solely from evils and falsities. When such a man, therefore, is left to himself and thinks from his spirit, he thinks from the affection of these loves, which he conjoins to the things that are in the Word; and when the Divine things of the Word are conjoined to such loves all things therein are adulterated and falsified, for the Divine things of the Word can never be conjoined to anything but celestial love, or with spiritual affection; if conjoined to any other love or any other affection, the higher mind, which is called the spiritual mind, is closed, and the lower mind only, which is called the natural mind, is opened; yea, with those who conjoin the truths of the Word to the affection of the love of self, the natural mind also is closed, and only the ultimate of this mind is opened, which is called the sensual, which clings most closely to the body, and stands forth nearest to the world. Thus does man's spirit become corporeal, and then it can have no lot with the angels, who are spiritual.