Genesis 35:1-4 And God said unto Jacob, Arise, go up to Bethel, and dwell there: and make there an altar unto God, that appeared unto thee when thou fleddest from the face of Esau thy brother. Then Jacob said unto his household, and to all that were with him, Put away the strange gods that are among you, and be clean, and change your garments: And let us arise, and go up to Bethel; and I will make there an altar unto God, who answered me in the day of my distress, and was with me in the way which I went. And they gave unto Jacob all the strange gods which were in their hand, and all their earrings which were in their ears; and Jacob hid them under the oak which was by Shechem.
Reading the account above, I often wondered if Jacob was an idolater. Did Abraham, Isaac, and Jacob worship stone idols in acts of idolatry? Some sages insist that the Divine Torah was not known to our fore-fathers until the time of Moses. Such sages say that the Noachide Law was in place, but not the full glory of YHWH's Law as delivered on Mount Sinai in Arabia. There is much evidence proving this wrong. The Law of Moses is eternal, existing from the time of Adam himself.
The answer to the riddle is found in the previous chapter of the Bible. Jacob's sons had just slaughtered the Shechemites for defiling their sister, Dinah.
Genesis 34:25-29 And it came to pass on the third day, when they were sore, that two of the sons of Jacob, Simeon and Levi, Dinah's brethren, took each man his sword, and came upon the city boldly, and slew all the males. And they slew Hamor and Shechem his son with the edge of the sword, and took Dinah out of Shechem's house, and went out. The sons of Jacob came upon the slain, and spoiled the city, because they had defiled their sister. They took their sheep, and their oxen, and their asses, and that which was in the city, and that which was in the field, And all their wealth, and all their little ones, and their wives took they captive, and spoiled even all that was in the house.
Notice that Israel took all the women and children of Shechem captive. They didn't go out and sell them, and they didn't kill them. These women all became a part of Jacob's family. The events at the beginning of this diary entry happened the very next day after the women were taken captive. Therefore it shows that Jacob would not tolerate idolatry in his house for even one day. The people of Shechem were terrible idolaters. Their most honorable man was a rapist and kidnapper.
Kidnapping carries the death penalty. Close study of the account of Dinah shows that when he went to negotiate with Jacob, he did it with Dinah in his possession. God's Law requires not only compensation when a man rapes a virgin, but the father of the virgin still retains his rights in her. The virgin does not belong to the man until the father consents to it. Shechem was a kidnapper. Rape of a virgin does not carry the death penalty, but kidnapping does. And dead Shechem was.
Leviticus 5:1 And if a soul sin, and hear the voice of swearing, and is a witness, whether he hath seen or known of it; if he do not utter it, then he shall bear his iniquity.
Why did Israel kill all the males of Shechem, instead of just Shechem himself? Group responsibility is an important concept in God's law. The men of Shechem were accessories to the crime. Shechem committed a crime. The men of the city had an obligation to find him guilty before a jury of his peers and to hand him over to Israel for punishment. If there were not enough righteous men in the city to do this, any righteous man had to at least public denounce the crime and distance himself from it. Since Shechem was the "most honorable" man in the city, it is obvious there were no righteous men who denounced his actions. This made all Shechemites accessories to the crime of rape and kidnap, and thus the penalty applied to all of them.