"2 Sa 12:8 your master’s wives. This phraseology means nothing more than that God in His providence had given David, as king, everything that was Saul’s. There is no evidence that he ever married any of Saul’s wives, though the harem of eastern kings passed to their successors. Ahinoam, the wife of David (2:2; 3:2; 1 Sam. 25:43; 27:3; 30:5), is always referred to as the Jezreelitess, whereas Ahinoam, the wife of Saul, is distinguished clearly from her by being called “the daughter of Ahimaaz” (1 Sam. 14:50)." MacArthur, J., Jr. (Ed.). (1997). The MacArthur Study Bible (electronic ed., p. 443). Nashville, TN: Word Pub.
And Nathan said to David, Thou art the man. Thus saith the LORD God of Israel, I anointed thee king over Israel, and I delivered thee out of the hand of Saul;
And I gave thee thy master’s house, and thy master’s wives into thy bosom, and gave thee the house of Israel and of Judah; and if that had been too little, I would moreover have given unto thee such and such things [2 Sam. 12:7–8].
"It took courage for Nathan to say this to David. In my judgment he is the bravest man in the Bible. I know of no one who can be compared to him. He said, “David, you are the guilty one.” What is David going to do? He is going to do something unusual, I can assure you of that. Dr. Margoliouth has said this: “When has this been done—before or since? Mary, Queen of Scots, would declare that she was above the law; Charles I would have thrown over Bathsheba; James II would have hired witnesses to swear away her character; Mohammed would have produced a revelation authorizing both crimes; Charles II would have publicly abrogated the seventh commandment; Queen Elizabeth would have suspended Nathan.” Years ago, the Duke of Windsor would have given up his throne for her. We have had some presidents who would have repealed the Ten Commandments and appointed Nathan to the Supreme Court. David did not do any of these things. His actions will reveal his greatness.
God would have given David anything his heart wanted, but David longed for something that was not his. The new morality today says it was not sin. God still says this is sin, and the man after God’s own heart cannot get by with it." McGee, J. V. (1997). Thru the Bible commentary (electronic ed., Vol. 2, p. 215). Nashville: Thomas Nelson.