Ish-bosheth Murdered; Mephibosheth

When Ish-bosheth hears of Abner's death "his hands were feeble, and all the Israelites were troubled." An aside: "Jonathan, Saul's son, had a son that was lame of his feet. He was five years old when the tidings came of Saul and Jonathan out of Jezreel, and his nurse took him up, and fled… he fell, and became lame. And his name was Mephibosheth."

Rechab and Baanah come in the heat of the day while Ish-bosheth lies on his bed, "and they smote him… and beheaded him," and walk all night with his head to Hebron. "Behold the head of Ishbosheth the son of Saul thine enemy."

"As the LORD liveth, who hath redeemed my soul out of all adversity, when one told me, saying, Behold, Saul is dead… I took hold of him, and slew him… How much more, when wicked men have slain a righteous person in his own house upon his bed?" They are executed and hanged by the pool in Hebron; Ish-bosheth's head is buried in Abner's tomb.

Mephibosheth

Mephibosheth (in Chronicles Merib-baal) was injured as a child in the panic after Gilboa. He is introduced here because he is the last possible heir of Saul's line, and he will matter in chapters 9, 16, 19 and 21. His disability is part of his story, not a moral lesson; the narrative later shows him both dependent and dignified.

Why the aside?

The note interrupts the murder story to show that with Ish-bosheth dead, Saul's house has no adult male heir to rival David.