John Calvin Commentary Genesis 34:13

"And the sons of Jacob answered Shechem and Hamor his father with guile, and spake, because he had defiled Dinah their sister," — Genesis 34:13 (ASV)

And the sons of Jacob answered. The beginning of their treacherous course is described here. For they, being enraged rather than simply angry, wish to overthrow the whole city. Not being strong enough to contend against such a large number of people, they devise a new fraud so that they may suddenly attack the inhabitants, who will be weakened by their wounds.

Therefore, since the Shechemites had no strength to resist, it became a cruel butchery rather than a conquest. This increased the atrocity of the wickedness of Jacob’s sons, who cared for nothing except to gratify their rage. As an excuse, they allege that, since they were separated from other nations, it was not lawful for them to give women of their own family to the uncircumcised.

This indeed was true, if they said it sincerely. But they falsely use the sacred name of God as a pretext. Indeed, their double profanation of that name proves them to be doubly sacrilegious, for they cared nothing about circumcision but were intent on this one thing: how they might crush these miserable men in their weakened state.

Besides, they wickedly sever the sign from the truth it represents, as if anyone, by casting off his uncircumcision, may suddenly enter the Church of God. In this way, they pollute the spiritual symbol of life by admitting foreigners into its fellowship promiscuously and without discrimination.

But since their pretense has some semblance of plausibility, we must note what they say: that it would be disgraceful for them to give their sister to an uncircumcised man. This also is true, if those who said this were sincere. For since they bore God's mark in their flesh, it was wicked for them to enter into marriages with unbelievers.

Similarly, at the present time, our baptism separates us from the profane, so that whoever mingles with them marks himself with infamy.