Calvin, on Judah’s command to Onan, his son, to go into his brother’s wife.
“Go in unto thy brother’s wife.”
Although no law had hitherto been prescribed concerning brother’s marriages, that the surviving brother should raise up seed to one who was dead; it is, nevertheless, not wonderful that, by the mere instinct of nature, men should have been inclined to this course. For since each man is born for the preservation of the whole race, if any one dies without children, there seems to be here some defect of nature. It was deemed therefore an act of humanity to acquire some name for the dead, from which it might appear that they had lived. Now, the only reason why the children born to the surviving brother, should be reckoned to him who had died, was, that there might be no dry branch in the family; and in this manner they took away the reproach of barrenness. Besides, since the woman is given as a help to the man, when any woman married into a family, she was, in a certain sense, given up to the name of that family. According to this reasoning, Tamar was not altogether free, but was held under an obligation to the house of Judah, to procreate some seed. Now, though this does not proceed from any rule of piety, yet the Lord had impressed it upon the hearts of man as a duty of humanity; as he afterwards commanded it to the Jews in their polity. Hence we infer the malignity of Onan, who envied his brother this honor, and would not allow him, when dead, to obtain the title of father; and this redounds to the dishonor of the whole family. We see that many grant their own sons to their friends for adoption: it was, therefore, an outrageous act of barbarity to deny to his own brother what is given even to strangers. Moreover he has not only shortened his brother concerning the right due to him, but he rather spilled seed on the ground than to raise a son in his brother’s name.