1 Samuel 20:5

the new moon The New Moon or first day of the lunar month was celebrated with special sacrifices and blowing of trumpets. See Numbers 28:11-15; Numbers 10:10; Psalms 81:3. It was observed as a day of rest (Amos 8:5), and apparently used as an opportunity for religious instruction (2 Kings 4:23).

to sit with the king at meat To join as a member of the royal household in the sacrificial feast (1 Samuel 20:24) which lasted for two days at least (1 Samuel 20:27).

let me go As the sequel proved, the plan was well devised for ascertaining whether the lesson of Naioth had wrought any change in Saul, or whether in his sane moments he was now deliberately resolved to kill David.