33. _Of Rebecca, the grand-daughter of Nahor, whom Isaac took to wife._
Isaac married Rebecca, the grand-daughter of Nahor, his father's brother, when he was forty years old, that is, in the 140th year of his father's life, three years after his mother's death. Now when a servant was sent to Mesopotamia by his father to fetch her, and when Abraham said to that servant, "Put thy hand under my thigh, and I will make thee swear by the Lord, the God of heaven, and the Lord of the earth, that thou shalt not take a wife unto my son Isaac of the daughters of the Canaanites,"[311] what else was pointed out by this, but that the Lord, the God of heaven, and the Lord of the earth, was to come in the flesh which was to be derived from that thigh? Are these small tokens of the foretold truth which we see fulfilled in Christ?
34. _What is meant by Abraham's marrying Keturah after Sarah's death._
What did Abraham mean by marrying Keturah after Sarah's death? Far be it from us to suspect him of incontinence, especially when he had reached such an age and such sanctity of faith. Or was he still seeking to beget children, though he held fast, with most approved faith, the promise of God that his children should be multiplied out of Isaac as the stars of heaven and the dust of the earth? And yet, if Hagar and Ishmael, as the apostle teaches us, signified the carnal people of the old covenant, why may not Keturah and her sons also signify the carnal people who think they belong to the new covenant? For both are called both the wives and the concubines of Abraham; but Sarah is never called a concubine (but only a wife). For when Hagar is given to Abraham, it is written, "And Sarai, Abram's wife, took Hagar the Egyptian, her handmaid, after Abram had dwelt ten years in the land of Canaan, and gave her to her husband Abram to be his wife."[312] And of Keturah, whom he took after Sarah's departure, we read, "Then again Abraham took a wife, whose name was Keturah."[313] Lo, both are called wives, yet both are found to have been concubines; for the Scripture afterward says, "And Abraham gave his whole estate unto Isaac his son. But unto the sons of his concubines Abraham gave gifts, and sent them away from his son Isaac, (while he yet lived,) eastward, unto the east country."[314] Therefore the sons of the concubines, that is, the heretics and the carnal Jews, have some gifts, but do not attain the promised kingdom; "For they which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed, of whom it was said, In Isaac shall thy seed be called."[315] For I do not see why Keturah, who was married after the wife's death, should be called a concubine, except on account of this mystery. But if any one is unwilling to put such meanings on these things, he need not calumniate Abraham. For what if even this was provided against the heretics who were to be the opponents of second marriages, so that it might be shown that it was no sin in the case of the father of many nations himself, when, after his wife's death, he married again? And Abraham died when he was 175 years old, so that he left his son Isaac seventy-five years old, having begotten him when 100 years old.