The sons of Jacob had come in from the field as soon as they heard of it, and the men were indignant and very angry, because he had done an outrageous thing in Israel by lying with Jacob’s daughter, for such a thing must not be done.
7. And the sons of Jacob came out of the field. Moses begins to relate the tragic issue of this history. Shechem, indeed, had acted wickedly and impiously; but it was far more atrocious and wicked that the sons of Jacob should murder a whole people, to avenge themselves of the private fault of one man.
Jacob's sons, when they heard of the injury done to Dinah, showed a very great resentment of it, influenced perhaps rather by jealousy for the honour of their family than by a sense of virtue. Many are concerned at the shamefulness of sin that never lay to heart the sinfulness of it.
Commenting on Genesis 34:6-17
And the sons of Jacob came out of the field, when they heard it,..... Either by a messenger Jacob sent to them, to acquaint them with it, or by some other hand: however, be it as it will, as soon as they heard of the abuse of their sister, they immediately left their flocks to the care of their servants, and came to their father's...