John Calvin Commentary Genesis 29:27

"Fulfil the week of this one, and we will give thee the other also for the service which thou shalt serve with me yet seven other years." — Genesis 29:27 (ASV)

Fulfil her week. Laban has now become callous in wickedness, for he extorts another seven years from his nephew to allow him to marry his other daughter. If he had had ten more daughters, he would have been ready to dispose of them all in this way: indeed, of his own accord, he thrusts forward his daughter as an object of merchandise, thinking nothing of the disgrace of this illicit sale, if only he may make it a source of gain.

In this, he truly sins grievously, in that he not only involves his nephew in polygamy but also pollutes both him and his own daughters with incestuous nuptials. If for any reason a wife is not loved by her husband, it is better to divorce her than for her to be retained as a captive and consumed with grief by the introduction of a second wife.

Therefore the Lord, through Malachi, pronounces divorce to be more tolerable than polygamy (Malachi 2:14). Laban, blinded by avarice, brings his daughters together in such a way that they spend their whole lives in mutual hostility. He also perverts all the laws of nature by casting two sisters into one marriage bed, so that the one becomes the competitor of the other.

Since Moses presents these crimes to the Israelites at the very beginning of their history, they should not be inflated with a sense of their nobility, leading them to boast of their descent from holy fathers. For, however excellent Jacob might have been, he had no other offspring than that which sprang from an impure source, since, contrary to nature, two sisters were brought together in one bed, in the manner of beasts, and two concubines were afterwards added to this situation.

Indeed, we have seen above that this license was too common among Eastern nations; but it was not permissible for men, at their own pleasure, to subvert by a depraved custom the law of marriage—divinely sanctioned from the beginning. Therefore, Laban is inexcusable in every way. And although necessity may, to some degree, excuse Jacob's fault, it cannot altogether absolve him from blame.

For he could have dismissed Leah, because she had not been his lawful wife, since mutual consent between the man and the woman—about which mistake is impossible—constitutes marriage. But Jacob reluctantly retains her as his wife, from whom he was released and free, and thus doubles his fault by polygamy and trebles it by an incestuous marriage. Thus we see that the excessive love for Rachel, which had once been aroused in his mind, was inflamed to such a degree that he possessed neither moderation nor judgment.

Regarding the words used, interpreters ascribe different meanings to them. Some refer the demonstrative pronoun to “the week”; others refer it to Leah, as if it had been said that Jacob should not have Rachel until he had lived with her sister for one week. But I prefer to explain it as referring to Rachel: that he should purchase a marriage with her by another seven years’ service. This does not mean that Laban deferred the wedding until the end of that time, but that Jacob was compelled to commit himself to a new period of servitude.