John Calvin Commentary Genesis 25:1

"And Abraham took another wife, and her name was Keturah." — Genesis 25:1 (ASV)

Then again Abraham took a wife. It seems very absurd that Abraham, who is said to have been dead in his own body thirty-eight years before the death of Sarah, should, after her death, marry another wife. Such an act was, certainly, unworthy of his dignity. Besides, when Paul commends his faith (Romans 4:19), he not only asserts that the womb of Sarah was dead when Isaac was about to be born, but also that the body of the father himself was dead.

Therefore, Abraham acted most foolishly if, after the loss of his wife, he, in the decrepitude of old age, entered into another marriage. Furthermore, it is inconsistent with Paul's statement that he, who in his hundredth year was cold and impotent, should, forty years later, have many sons.

Many commentators, to avoid this absurdity, suppose Keturah was the same person as Hagar. But their conjecture is immediately refuted in the context, where Moses says Abraham gave gifts to the sons of his concubines. The same point is clearly established from 1 Chronicles 1:32. Others conjecture that, while Sarah was still alive, he took another wife.

This, although worthy of grave censure, is, however, not entirely incredible. We know it is not uncommon for men to be emboldened by excessive license. Thus, Abraham, having once transgressed the law of marriage, perhaps, after the dispute concerning Hagar, did not desist from the practice of polygamy.

It is also probable that his mind had been wounded by the divorce from Hagar that Sarah had compelled him to carry out. Such conduct, indeed, was disgraceful or, at least, unbefitting the holy patriarch. Nevertheless, of all the conjectures that have been made, no other seems more probable to me.

If this is admitted, the narrative chronologically belongs elsewhere, for Moses frequently arranges material out of strict chronological order. And even if this reason is not considered conclusive, the facts themselves indicate a reversed order in the history. Sarah was past her ninetieth year when she gave birth to her son Isaac; she died at the age of one hundred and twenty-seven; and Isaac married when he was forty years old.

Therefore, nearly four years passed between the death of his mother and his marriage. If Abraham took a wife after this, what was he thinking, considering he had been accustomed to a single life for so many years? It is therefore reasonable to conjecture that Moses, in writing the life of Abraham, when he approached the end of Abraham's life story, inserted what he had previously omitted.

The difficulty, however, is not yet solved. For what was the source of Abraham’s renewed vigor, since Paul testifies that his body had long ago been withered by age? Augustine supposes not only that strength was given to him for a short time, which would be sufficient for Isaac’s birth, but that by a divine restoration, it flourished again for the rest of his life.

This opinion I willingly embrace, both because it magnifies the glory of the miracle and for other reasons. And what I have previously said, namely, that Isaac was miraculously born as a spiritual seed, is not contrary to this view, for it was especially on his account that Abraham’s failing body was restored to vigor.

That others were born later was, so to speak, incidental. Thus the blessing of God pronounced in the words Increase and multiply, which was specifically linked to marriage, is also extended to unlawful unions. Certainly, if Abraham married a wife while Sarah was still alive (as I think most probable), his adulterous union was unworthy of the divine blessing.

But although we do not know why this addition was made to the just measure of favor granted to Abraham, yet the wonderful providence of God appears in this: while many nations of considerable importance descended from his other sons, the spiritual covenant, of which the others also bore the sign in their flesh, remained in Isaac’s exclusive possession.