CONCUBINE
Secondary category wife.
Sometimes slaves given by wives to their husbands to have offspring (Gen. 16:2, 3; 39:29); It was not, however, the main reason for taking concubines. Deut. 21:11 gives the root of this practice: a man saw a beautiful woman, and lusted after her.
God seems to have simply allowed it for the same reason that the Lord Jesus states about the ease of giving the bill of divorce: “because of the hardness of your heart” (Mt. 19:8).
The kings of Israel are forbidden to multiply wives, lest they lead their hearts astray (Deut. 17:17). This was the cause of Solomon’s fall (1 Kings 11:3). In Esther 2:14 and Dan. 5:2 it is seen that concubinage was also a custom among the Gentiles.
Christianity denounces this evil, recognizing the monogamous marital relationship as God established it “in the beginning” (Gen. 2:23, 24; cp. Mt. 19:8, 9; 1 Tim. 3:2, 12; Tit. 1:6), and therefore the sanctity of the marriage bond in those whom God has joined together.