Puritan Board Doctor
If brethren dwell together, and one of them die. This law has some similarity with that which permits a betrothed person to return to the wife, whom he has not yet taken; since the object of both is to preserve to every man what he possesses, so that he may not be obliged to leave it to strangers, but that he may have heirs begotten of his own body: for, when a son succeeds to the father, whom he represents, there seems to be hardly any change made. Hence, too, it is manifest how greatly pleasing to God it is that no one should be deprived of his property, since He makes a provision even for the dying, that what they could not resign to others without regret and annoyance, should be preserved to their offspring. Unless, therefore, his kinsman should obviate the dead man’s childlessness, this inhumanity is accounted a kind of theft. For, since to be childless was a curse of God, it was a consolation in this condition to hope for a borrowed offspring, that the name might not be altogether extinct.
Since we now understand the intention of the law, we must also observe that the word brethren does not mean actual brothers, but cousins, and other kinsmen, whose marriage with the widows of their relative would not have been incestuous; otherwise God would contradict Himself. But these two things are quite compatible, that no one should uncover the nakedness of his brother, and yet that a widow should not marry out of her husband’s family, until she had raised up seed to him from some relation. In fact, Boaz did not marry Ruth because he was the brother of her deceased husband, but only his near kinsman. If any should object that it is not probable that other kinsmen should dwell together, I reply that this passage is improperly supposed to refer to actual living together, as if they dwelt in the same house, but that the precept is merely addressed to relations, whose near residence rendered it convenient to take the widows to their own homes; for, if any lived far away, liberty was accorded to both to seek the fulfillment of the provision elsewhere. Surely it is not probable that God would have authorized an incestuous marriage, which He had before expressed His abomination of. Nor can it be doubted, as I have above stated, but that the like necessity was imposed upon the woman of offering herself to the kinsman of her former husband; and although there was harshness in this, still she seemed to owe this much to his memory, that she should willingly raise up seed to the deceased; yet, if any one think differently, I will not contend the point with him. If, however, she were not obliged to do so, it was absurd that she should voluntarily obtrude herself: nor was there any other reason why she should bring to trial the kinsman, from whom she had suffered a repulse, except that she might acquire the liberty of marrying into another family. Yet it is not probable that he was to be condemned to an ignominious punishment, without being admitted to make his defense, because sometimes just reasons for refusal might be alleged. This disgrace, therefore, was only a penalty for inhumanity or avarice. By giving up his shoe, he renounced his right of relationship, and gave it up to another: for, by behaving so unkindly towards the dead, he became unworthy of reaping any of the advantages of his relationship.(Calvin, Harmony of the Four Last Books of Moses)
Calvin here on Deuteronomy 25:5-10 indicates that he does not believe that this passage applies to brothers but near relations because the law here would contradict Leviticus 18:16:
Thou shalt not uncover the nakedness of thy brother's wife: it is thy brother's nakedness.(Lev 18:16)
Was Calvin right on this, or not?
His relevant comment on the "case" brought by the Sadducees to "test" Christ in Matthew 22:23-33, Mark 12:18-27 and Luke 20:27-40 is:
With respect to the law, (Deuteronomy 25:5,) by which God commanded the relatives, who were nearest of kin, to succeed the dead in marriage, if the first had died without children, the reason was, that the woman who had married into a particular family should leave offspring in it. But if there had been children by the first marriage, a marriage within the degrees forbidden by the law (Leviticus 18:16) would have been incestuous. (Calvin, Harmony of the Gospels)