John Gill's Bible Commentary Ver. 4. Now when Jehoram was risen up to the kingdom of his father , etc.] Succeeded him in it, and reigned alone, for he had reigned with his father some years before his death; (See Gill on “ 2 Kings 8:16”), he strengthened himself ; in the kingdom, by some means or another closely attaching the greater part of the princes, and people of the land, unto him, when he thought himself well settled and established on the throne; though some understand it of making strong, or hardening his heart to do what is next mentioned: and slew all his brethren with the sword ; either to get their riches into his hands, or lest, being religious princes, they should oppose his restoring idolatry, and for that reason the people should depose him, and set up one of them; and therefore he dispatched them out of the way to secure himself, and carry his point: and [divers] also of the princes of Israel ; such who had removed out of the ten tribes, for the sake of religion, and therefore would never agree to the introduction of idolatry among them, for which reason Jehoram slew them; and perhaps they might express their disapprobation and abhorrence of his murder of his brethren.
Matthew Henry Commentary
Verses 1-11 - Jehoram hated his brethren, and slew them, for the same reason tha Cain hated Abel, and slew him, because their piety condemned his impiety. In the mystery of Providence such men sometimes prosper for time; but the Lord has righteous purposes in permitting such events part of which may now be made out, and the rest will be seen hereafter.
Original Hebrew ויקם6965 יהורם3088 על5921 ממלכת4467 אביו1 ויתחזק2388 ויהרג2026 את853 כל3605 אחיו251 בחרב2719 וגם1571 משׂרי8269 ישׂראל׃3478