A concubine, according to the ancient custom, was the wife of a man, who had more than one wife. She was dubbed a concubine, because she was a secondary wife and subservient to the main wife. In other words, although Abraham took Hagar to be his wife (Genesis 16:1-3), she was actually supposed to remain submissive to Sarah, Abraham’s main wife, besides which Hagar was originally Sarah’s handmaid (Genesis 16:1). When Hagar magnified her position (Genesis 16:4) and Sarah complained to Abraham, he told Sarah that she had the right to treat Hagar as she pleased (Genesis 16:5-6), vis-à-vis, although Hagar was Abraham’s wife, she was also considered to be Sarah’s servant. In other words, Sarah, Abraham’s main wife, ruled her husband’s household, which included his concubines and their children. A concubine was more than an ordinary servant, but she was still considered to be under the authority of the main wife of the household.
We are told in the text that Abraham had taken a wife once again, and her name was Keturah, vis-à-vis Keturah was taken after Hagar (Genesis 25:1). It isn’t specifically said in the text, but Keturah was a concubine, and the union took place, while Sarah was still alive. The fact that she is a concubine is implied in verse-6, and clearly stated in 1Chronicles 1:32. Moreover, since she is a concubine, it is implied that there was a main wife to whom she must submit. Therefore, the marriage between Abraham and Keturah had to have taken place prior to Sarah’s death, otherwise Keturah would have been the then current main wife.
This union gave Abraham six more sons and eleven grandchildren and greatgrandchildren (Genesis 25:2-4). No women are mentioned, but this doesn’t mean the marriage didn’t produce any daughters. However, Isaac stood to inherit not only the promises the Lord made to Abraham, but also all of the wealth Abraham had, his entire estate (Genesis 25:5). None of the children of Abraham’s concubines stood to inherit the promises. In fact, prior to his death, Abraham sent both his concubines and their children away, and he gave them gifts. Nevertheless, none of his children by Hagar or Keturah would inherit his wealth (Genesis 25:6; cp. 21:10). Thus, since no other women are mentioned, whom Abraham had taken as a wife/concubine, Hagar and Keturah are the concubines meant in verse-6. Moreover, it is implied here that Abraham had also given Ishmael gifts, when he sent him away (Genesis 25:6; cp. 21:14).
Finally, we are told that Abraham died of a good old age, full of years (or full of days), at 175 years (Genesis 25:7-8; cp. Genesis 15:15).[1] And, he “was gathered to his people,” vis-à-vis slept with his fathers (cp. Deuteronomy 31:16). Isaac and Ishmael buried him in the cave, where Sarah was buried, at the end of the field, which Abraham purchased from the sons of Heth (Genesis 25:9-10).
Afterward, Isaac continued to dwell in the south country near the well, Lahairoi, which is the well where the Angel of the Lord appeared to Hagar, when she fled from Sarah, her mistress (Genesis 25:11, cp. 16:14). As for Ishmael, Abraham’s son by Hagar, the Egyptian woman, he lived to be 137 years old, and he died in the presence of his brethren, vis-à-vis in the presence of Isaac and the sons of Keturah. He begat twelve sons, princes, according to their nations, and they dwelt from Havilah, close to where the Euphrates joins the Tigris River in the east, to Shur in the west, which is just before entering Egypt, at the isthmus of Suez, which separates the Mediterranean Sea from the Red Sea (Genesis 25:12-18).
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[1] According to Clarke’s Commentary, the expression full of years/days is an expression meaning he died without regret. It seems to be a metaphor taken from how a guest feels after partaking of a plentiful banquet.