Charles Ellicott Commentary Genesis 34:25

"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 unawares, and slew all the males." — Genesis 34:25 (ASV)

Simeon and Levi, Dinah’s brothers.—As born of the same mother, they, along with Reuben and Judah, were especially bound to champion their sister’s cause, but the method they took was extremely cruel. And it seems that these two were the leaders in the plot, having probably excluded Reuben from it, as a man of weak character and opposed to bloodshed (Genesis 37:22); and Judah, as one too honorable to take part in such a nefarious deed.

Long afterwards, Jacob spoke of it in terms of the strongest condemnation (Genesis 49:5–7). In executing their cruel deed, they would have commanded the services of the more active and fierce portion of Jacob’s servants; but they must have been not boys, but men of mature manhood, before they could have had influence or power enough for so terrible an undertaking.