2-а Самуїлова 16:21

Ahithophel gave the following counsel: "Go to thy father's concubines, whom he hath left behind to keep the house (i.e., lie with them: for אל בּוא, compare Sa2 3:7, etc.); so will all Israel hear that thou hast made thyself stinking with thy father, and the hands of all those who are with thee will strengthen themselves." This advice was sagacious enough. Lying with the king's concubines was an appropriation of the royal harem, and, as such, a complete usurpation of the throne (see at Sa2 3:7), which would render any reconciliation between Absalom and his father utterly impossible, and therefore would of necessity instigate the followers of Absalom to maintain his cause with all the greater firmness. This was what Ahithophel hoped to attain through his advice. For unless the breach was too great to be healed, with the affection of David towards his sons, which might in reality be called weakness, it was always a possible thing that he should forgive Absalom; and in that case Ahithophel would be the one to suffer. But under the superintendence of God this advice of Ahithophel was to effect the fulfilment, without any such intention on his part, of the threat held over David in Sa2 12:8.

In the close of the foregoing chapter we left David flying from Jerusalem, and Absalom entering into it; in this chapter, I. We are to follow David in his melancholy flight; and there we find him, 1. Cheated by Ziba (Sa2 16:1-4). 2. Cursed by Shimei, which he bears with wonderful patience (Sa2 16:5-14). II. We are to meet Absalom in his triumphant entry; and there we find him, 1. Cheated by Hushai (Sa2 16:15-19). 2. Counselled by Ahithophel to go in unto his father's concubines (Sa2 16:20-23).

16:21 Go and sleep with your father’s concubines: A usurper took a predecessor’s harem to assert or strengthen his claim to the throne (see 3:7). Absalom’s action was in violation of Deut 22:30.