What does Genesis 34:25 mean?

The town is home to Hamor, the local prince, and his son, Shechem. Jacob and his massive clan had recently moved into the area (Genesis 34:18–19). Unfortunately, Shechem chose to attack and rape Dinah, Jacob's daughter (Genesis 34:1–3). When he and his father came to negotiate to marry Dinah (Genesis 34:8–12), her brothers lied in order to set up this massacre (Genesis 34:13). They claimed that if all the men of town were circumcised, they'd be open to free trade and intermarriage (Genesis 34:14–16). Their actual intent was revenge, but it worked, and the townspeople agreed (Genesis 34:20–24).

Circumcision involves cutting away the foreskin: a flap of tissue covering the end of the penis. This is typically done soon after birth, when it's relatively quick and easy. Circumcising an adult male involves significant discomfort and a longer recovery time. Jacob's sons know exactly what the recovery process is like, and they've planned accordingly. By the third day, their enemies are suffering the full effects. When the attack comes, the fighting men are partly disabled—preoccupied with pain and in no condition for combat.

The result is a brutal and catastrophic revenge that goes far beyond paying back the original crime. Shechem, Hamor, and the men of the city had trusted Jacob's family. They expected to reap financial benefits from their circumcision, but that day never came. When the people of the city felt most secure, Simeon and Levi lead a surprise attack and slaughtered every adult male. Most likely, this assault was carried out by more than just the two brothers—a full-scale attack such as this would have included their respective servants, as well.

It should be noted that Simeon and Levi are sons of Jacob's first wife, Leah, who is also the natural mother of Dinah. Jacob's outright favoritism (Genesis 29:31) may have played a role in their choice to respond with such violence.