1 Kings 2:15

Thou knowest. — Adonijah’s words show craft, flattering Bath-sheba by extolling her influence, and making merit of his surrender to Solomon, in obedience to the Lord’s decree, of a kingdom which, in evident contradiction to fact, he asserts to have been destined to him by popular desire. The petition, however, apparently harmless, and (since Abishag was concubine of David only in name) involving nothing unnatural, had perhaps a covert design: for, by universal Eastern custom, to take a king’s wives was the known privilege or duty of his successor. Hence the counsel, most unseemly but still probably politic, given by Ahithophel to Absalom (2 Samuel 16:21). If, therefore, Adonijah had publicly espoused Abishag, it might have seemed a virtual renewal of his claim to the crown. This Solomon sees at once, though Bath-sheba, strangely enough, does not see it.