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.

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

753. For the devil is come down unto you.- That this signifies, because they receive evils from hell, is evident from the signification of the devil, as denoting that hell from which evils come (concerning which see above, n. 740); and from the signification of coming down unto them, when said of the devil, as denoting to be among them, to seduce them, and to be received by them. Those to whom the devil came down mean those that inhabit the earth and the sea, and these signify those who are merely natural and sensual, who became such because they rejected the life of faith, which is called charity. Those who reject this because of their religion, and who believe and say in their heart that deeds contribute nothing to salvation, but that faith alone and piety in worship save, remain natural, and even become sensual, so far as they reject goods in act or deed, and give themselves up to the pleasures that spring from the loves of self and of the world. Because such remain natural, and even become sensual, they receive with delight the evils that arise out of hell; for the natural man is in those evils from birth, and unless he also becomes spiritual, he continues in them. For when a man becomes spiritual he has communion with the heavens, and receives goods therefrom, and the goods received from the Lord through heaven remove evils, and this is effected entirely by a life according to the commandments from the Word.