I will shoot three arrows - Jonathan intended that David should stay at the stone Ezel, where probably there was some kind of cave, or hiding place; that, to prevent all suspicion, he would not go to him himself, but take his servant into the fields, and pretend to be exercising himself in archery; that he would shoot three arrows, the better to cover his design; and that, if he should say to his servant, who went to bring back the arrows, "The arrows are on this side of thee," this should be a sign to David that he might safely return to court, no evil being designed; but if he should say, "The arrows are beyond thee," then David should escape for his life, Saul having determined his destruction.

1 Samuel 20:19 "When you have stayed for three days, you shall go down quickly and come to the place where you hid yourself on that eventful day, and you shall remain by the stone Ezel.

1 Samuel 20:21 "And behold, I will send the lad, saying, 'Go, find the arrows.' If I specifically say to the lad, 'Behold, the arrows are on this side of you, get them, ' then come; for there is safety for you and no harm, as the LORD lives.

Samuel
Alike from the literary and the historical point of view, the book[1] of Samuel stands midway between the book of Judges and the book of Kings. As we have already seen, the Deuteronomic book of Judges in all probability ran into Samuel and ended in ch. xii.; while the story of David, begun in Samuel, embraces the first two chapters of the first book of Kings. The book of Samuel is not very happily named, as much of it is devoted to Saul and the greater part to David; yet it is not altogether inappropriate, …
John Edgar McFadyen—Introduction to the Old Testament