Charles Ellicott Commentary 1 Samuel 20:18

"Then Jonathan said unto him, To-morrow is the new moon: and thou wilt be missed, because thy seat will be empty." — 1 Samuel 20:18 (ASV)

You will be missed. — "Well then," resumes Jonathan—after the passionate conclusion of the solemn covenant between the friends—"the last trial will be as you propose. At the State banquet of my father tomorrow your seat, as agreed upon, will be empty; then you and I—when King Saul misses you—will know the worst."