Against his own life - Adonijah had forfeited his life by his former conduct, and his pardon had been merely conditional 1 Kings 1:52.

Then King Solomon sware by the Lord,.... To prevent his mother pressing him to have her petition granted:

saying, God do so to me, and more also; lay such and such evils upon me, and more than I care to express:

if Adonijah have not spoken this word against his own life; to his own prejudice, and even to the loss of his life; in which Solomon suggests it would issue, being a fresh overt act of treason; he knew, from what Bathsheba said, that this was his petition, and that he had spoken of this to her, and put her upon making it for him; and who no doubt related to Solomon the whole of the conversation that passed between them, and to which he seems to have some respect in his answer.

Solomon thereupon solemnly swore (the formula of an oath, and the כּי introducing the oath, as in 1 Samuel 14:44, etc.), "Adonijah has spoken this word against his own life." בּנפשׁו, at the cost of his life, as in 2 Samuel 23:17, i.e., at the hazard of his life, or to his destruction. 2 Samuel 23:24. "And now, as truly as Jehovah liveth, who hath established me and set me on the throne of my father David, and hath made me a house, as He said (verbatim, 2 Samuel 7:11): yea, to-day shall Adonijah be put to death." Jehovah established Solomon, or founded him firmly, by raising him to the throne in spite of Adonijah's usurpation. In ויושׁיביני the central י has got into the text through a copyist's error. בּית לי עשׂה, i.e., He has bestowed upon me a family or posterity. Solomon had already one son, viz., Rehoboam, about a year old (compare 1 Kings 11:42 with 1 Kings 14:21 and 2 Chronicles 12:13).

(Note: When Thenius denies this, and maintains that Rehoboam cannot have been 41 years old when he began to reign, referring to his discussion at 1 Kings 14:21, he answers himself, inasmuch as at 1 Kings 14:21 he demonstrates the fallacy of the objections which Cappellus has raised against the correctness of the reading "41 years.")

Then king Solomon sware by the LORD, saying, God do so to me, and more also, if Adonijah have not spoken this word against his own life.

23-25. God do so to me, and more also-the common form of introducing a solemn oath.

if Adonijah have not spoken this word against his own life-Whether there was a treasonable design to conceal under this request or not, the act, according to Eastern notions, was criminal, and of dangerous consequence to the state. There is no ground of censure upon Solomon for cruelty or precipitation in this instance. He had pardoned Adonijah's former conspiracy; but this new attempt was rebellion against the viceroy appointed by the divine King and called for condign punishment. The office of executioner was among the Hebrews, as in other ancient countries of the East, performed unceremoniously and privately-often without any previous warning-by the captain of the guard, or one of his officers (Mt 14:10).

2:12-25 Solomon received Bathsheba with all the respect that was owing to a mother; but let none be asked for that which they ought not to grant. It ill becomes a good man to prefer a bad request, or to appear in a bad cause. According to eastern customs it was plain that Adonijah sought to be king, by his asking for Abishag as his wife, and Solomon could not be safe while he lived. Ambitious, turbulent spirits commonly prepare death for themselves. Many a head has been lost by catching at a crown.