2 Chronicles 21:4 Commentary - English Annotations on the Holy Bible by Matthew Poole

He strengthened himself; he took courage and hardened his heart, as that word sometimes signifies.

Slew all his brethren with the sword; partly because they either did, or he knew that they would, oppose him in his wicked designs; and partly for his own security, lest his people, who, as he believed, would be highly exasperated with the execution of his counsels, should advance any of them to the throne, and depose him.

Of the princes of Israel; either,

1. Of Judah, here called Israel, or which See Poole "2Ch 21:2". Or,

2. The princes or chief men of Israel, properly so called; not the princes of all Israel, or of the several tribes thereof, but the chief of those Israelites who, out of love to God and to the true religion, had forsaken their estates and worthy advantages in the kingdom of Israel, and were now incorporated with the kingdom of Judah. These he especially struck at, either,

1. Because his wife instigated him thereunto, both to punish them for their revolt from her father, and to deter others from following their example. Or,

2. Because he justly and truly thought these would be most firm and constant to and zealous for that religion which he was resolved to oppose, being both by their conscience and interest obliged to it.