There fell. — The regular term for desertion of one cause for another (2 Kings 25:11).
When he came with the Philistines. — (Comp. 1 Samuel 29:2-11.) This verse is a summary of the narrative of 1 Samuel 29:2 to 1 Samuel 30:1.
They helped them not. — David and his men helped not the Philistines. Perhaps the right reading is he helped them (‘azarâm), not they helped them (‘azarûm).
Upon advisement. — After deliberation (Proverbs 20:18).
To the jeopardy of our heads. — At the price of our heads (1 Chronicles 11:19). By betraying us he will make his peace with his old master.