v1, The news of general Abner's death crushed Ish-bosheth's hope of continuing his father, Saul's reign. It also gravely shocked the Israelites who lived north of Judah and who were attached to Ish-bosheth’s reign. Bad news can greatly affect and dishearten us.
V2-3 here the writer wanted to make the very sharp point that Baanah and Rechab were Benjamites—from Saul's own tribe. His own blood!
V4, Mephobosheth is introduced here as Jonathan’s son (a potential heir to Saul’s throne, but disqualified because of his youth and his inability to lead militarily). This is the setup for ch 9.
V5-8, The ugly assassination and regicide of Ish-bosheth.
V9-12, Notice that the two assassins appeal to the Lord’s will here. But David has learned his lesson about respect for ordained authority, a lesson we can all take to heart as the Lord’s children. This touches on reverence/respect for government, family and church leadership and more. Just because someone invokes the name of the Lord doesn’t make them right. See 1 Sam 24:4-5 & 26:8-11