Мусар к Берешит 25:19

How pleasant is the Musar of Love. Anyone whom Hashem loves, God brings down upon them suffering. You find three good gifts that God gave to Israel; and they were only given by way of suffering. These are them: Torah, the Land of Israel, and the World to Come.

First of all, the universe was created for the sake of man who was formed in the image and likeness, i.e. בצלם ודמות of G–d, so to speak. This means that אדם התחתון is patterned after אדם העליון, a heavenly version of man. This means that not only his heavenly counterpart but also he himself is holy, or that "the book and the cover" are both holy. The book and the cover in this instance are the soul and the body. When in such a state, man's clothing are כתנות אור, garments woven of the original light with which G–d created the universe. The word דמות describes the holiness of the body, whereas the word צלם describes the state of man's soul. We have discussed this at length in the treatise תולדות אדם. As long as such ideal conditions prevailed man's immortality was not limited to his species, but each individual person enjoyed everlasting life. The system of procreation would have paralleled that of the angels who develop from one another much like a candle which can light another without the light of the original candle thereby decreasing or “aging.” As a result of this type of procreation G–d's צלם would have expanded continuously, each new human being would have had the צלם אלוקים transmitted to it with the drop of semen it originated from, though such a human being had not been formed by G–d Himself as had Adam. The drop of semen would not then have been described as "an evil smelling drop," as it is described nowadays in Avot 3,1.

In view of these statements, we need to learn more about how the serpent and its evil influence began. The ability of the serpent to seduce is rooted in the power of Samael who rode it. Samael is the spirit of זנונים, lechery, whose lecherous feelings were aroused by the sight of Adam and Eve copulating. The serpent which used to walk on legs was punished by having its legs cut off. The thigh joint (to which the legs are attached) is within the domain of the sexual organs. Esau had the likeness of a snake as a birthmark on his thigh, as we have mentioned in Parshat Toldot. The Israelites, on the other hand, are holy, abstain from eating the גיד הנשה, and Bileam (Numbers 23, 23) testified already “כי לא נחש ביעקב, Israel is not infected by the serpent."