Genesis 25:1

Then again Abraham took a wife - When Abraham took Keturah we are not informed; it might have been in the lifetime of Sarah; and the original ויסף vaiyoseph , and he added, etc., seems to give some countenance to this opinion. Indeed it is not very likely that he had the children mentioned here after the death of Sarah; and from the circumstances of his age, feebleness, etc., at the birth of Isaac, it is still more improbable. Even at that age, forty years before the marriage of Isaac, the birth of his son is considered as not less miraculous on his part than on the part of Sarah; for the apostle expressly says, Romans 4:19 , that Abraham considered not his own body Now Dead, when he was about a hundred years old, nor the Deadness of Sarah's womb; hence we learn that they were both past the procreation of children, insomuch that the birth of Isaac is ever represented as supernatural. It is therefore very improbable that he had any child after the birth of Isaac; and therefore we may well suppose that Moses had related this transaction out of its chronological order, which is not infrequent in the sacred writings, when a variety of important facts relative to the accomplishment of some grand design are thought necessary to be produced in a connected series. On this account intervening matters of a different complexion are referred to a future time. Perhaps we may be justified in reading the verse: "And Abraham had added, and had taken a wife (besides Hagar) whose name was Keturah," etc. The chronology in the margin dates this marriage with Keturah A. M. 2154, nine years after the death of Sarah, A. M. 2145. Jonathan ben Uzziel and the Jerusalem Targum both assert that Keturah was the same as Hagar. Some rabbins, and with them Dr. Hammond, are of the same opinion; but both Hagar and Keturah are so distinguished in the Scriptures, that the opinion seems destitute of probability.