1 KINGS 2
23 Then king Solomon sware by Yahweh, saying, Elohim do so to me, and more also, if Adonijah have not spoken this word against his own life.
The Sin of Adonijah
-Adonijah was put to death because Solomon regarded his asking for Abishag as a re-assertion of his claim to the throne. Upon the occasion of his attempted usurpation, Solomon pardoned him on condition that he proved himself a worthy man (1 Sam. 1:5, 52).
He had now evidently lost all faith in him. If Adonijah's object was to re-open his assumed claim to the throne, or to get a footing in the royal house, the better to promote his plans; as Solomon's verdict seems to imply, then he was worthy of death. It was "the word" that Adonijah had spoken through Bathsheba that cost him his life.
The Christadelphian, Mar 1888
27 So Solomon thrust out Abiathar from being priest unto Yahweh; that he might fulfil the word of Yahweh [1 Sam 2: 33], which he spake concerning the house of Eli in Shiloh.
One man of the line of lthamar escaped, as young Abiathar, the son of Ahimelech joined David's band, bringing with him the High Priest's ephod. Yet this survivor was also caught within the measure of the curse, and his end would not escape the reach of the divine judgment. Although he laboured with David, circumstances brought about a disengagement between the two men, which in the course of time led to a rupture of trust, and a revealing of the spirit of treachery in Abiathar.
The final degradation of Eli's house was made complete in the decision of Solomon to thrust out Abiathar from being priest before the Lord. Solomon's action, in response to Abiathar's betrayal of David in supporting the rebellion of Adonijah, led to his exile in disgrace to Anathoth.
With this final banishment, the judgment against the house of Eli was made complete, in a man who although not initially cut off from the altar, would only serve to cause grief to Eli (had he been alive to see it), and shame to Abiathar who was alive to know it.
Bro Roger Lewis - Hannah Handmaid of the Highest Ch 7