For the fetus, though enclosed in the womb of its mother, is already a human being, and it is a monstrous crime to rob it of the life which it has not yet begun to enjoy. If it seems more horrible to kill a man in his own house than in a field, because a man’s house is his place of most secure refuge, it ought surely to be deemed more atrocious to destroy a fetus in the womb before it has come to light.

John Calvin
Commentary, Exodus 21:22.