His concubine - We borrow this word from the Latin compound concubina, from con, together, and cubo, to lie, and apply it solely to a woman cohabiting with a man without being legally married. The Hebrew word is פילגש pilegesh, which is also a compound term, contracted, according to Parkhurst, from פלג palag, to divide or share, and נגש nagash, to approach; because the husband, in the delicate phrase of the Hebrew tongue, approaches the concubine, and shares the bed, etc., of the real wife with her. The pilegesh or concubine, (from which comes the Greek παλλακη pallake, and also the Latin pellex), in Scripture, is a kind of secondary wife, not unlawful in the patriarchal times; though the progeny of such could not inherit. The word is not used in the Scriptures in that disagreeable sense in which we commonly understand it. Hagar was properly the concubine or pilegesh of Abraham, and thus annuente Deo, and with his wife's consent. Keturah, his second wife, is called a concubine, Genesis 26:15; 1-Chronicles 1:32; and Pilhah and Zilhah were concubines to Jacob, Genesis 35:22. After the patriarchal times many eminent men had concubines, viz., Caleb, 1-Chronicles 2:46, 1-Chronicles 2:48; Manasses, 1-Chronicles 7:14; Gideon, Judges 8:31; Saul, 2-Samuel 3:7; David, 2-Samuel 5:13; Solomon,2-Kings 11:3; and Rehoboam, 2-Chronicles 11:21. The pilegesh, therefore, differed widely from a prostitute; and however unlawful under the New Testament, was not so under the Old.
From this chapter a pious mind may collect much useful instruction. From the trial of Abraham we again see, 1. That God may bring his followers into severe straits and difficulties, that they may have the better opportunity of both knowing and showing their own faith and obedience; and that he may seize on those occasions to show them the abundance of his mercy, and thus confirm them in righteousness all their days. There is a foolish saying among some religious people, which cannot be too severely reprobated: Untried grace is no grace. On the contrary, there may be much grace, though God, for good reasons, does not think proper for a time to put it to any severe trial or proof. But grace is certainly not fully known but in being called to trials of severe and painful obedience. But as all the gifts of God should be used, (and they are increased and strengthened by exercise), it would be unjust to deny trials and exercises to grace, as this would be to preclude it from the opportunities of being strengthened and increased. 2. The offering up of Isaac is used by several religious people in a sort of metaphorical way, to signify their easily-besetting sins, beloved idols, etc. But this is a most reprehensible abuse of the Scripture. It is both insolent and wicked to compare some abominable lust or unholy affection to the amiable and pious youth who, for his purity and excellence, was deemed worthy to prefigure the sacrifice of the Son of God. To call our vile passions and unlawful attachments by the name of our Isaac is unpardonable; and to talk of sacrificing such to God is downright blasphemy. Such sayings as these appear to be legitimated by long use; but we should be deeply and scrupulously careful not to use any of the words of God in any sense in which he has not spoken them. If, in the course of God's providence, a parent is called to give up to death an amiable, only son, then there is a parallel in the case; and it may be justly said, if pious resignation fill the parent's mind, such a person, like Abraham, has been called to give his Isaac back to God.
Independently of the typical reference to this transaction, there are two points which seem to be recommended particularly to our notice. 1. The astonishing faith and prompt obedience of the father. 2. The innocence, filial respect, and passive submission of the son. Such a father and such a son were alone worthy of each other.

And his (i) concubine, whose name [was] Reumah, she bare also Tebah, and Gaham, and Thahash, and Maachah.
(i) Concubine is often used to refer to those women who were inferior to the wives.

And his concubine, whose name was Reumah,.... Not an harlot, but a secondary wife, who was under the proper and lawful wife, and a sort of a head servant in the family, and chiefly kept for the procreation of children; which was not thought either unlawful or dishonourable in those times such as was Hagar in Abraham's family:
she bare also Tebah, and Gaham, and Thahash, and Maachah, of whom we have no account elsewhere; only it may be observed, that here Maachah is the name of a man, which sometimes is given to a woman, 1-Kings 15:13.