1 Samuel 20:5
And David said unto Jonathan, Behold, to morrow is the new moon, and I should not fail to sit with the king at meat: but let me go, that I may hide myself in the field unto the third day at even. And David said unto Jonathan, Behold, to morrow is the new moon, and I should not fail to sit with the king at meat: but let me go, that I may hide myself in the field unto the third day at even.
The verse belongs to the time after David killed Goliath, when Saul kept David with him and would not let him return to his father's house. At that time Jonathan's soul was knit to David's, loving him as his own soul, and they made a covenant to be united as brothers. In token of that covenant Jonathan gave David his robe and his garments, along with his sword and his bow and his girdle. Their sacred bond remained unbroken and helped preserve David's life when Saul tried to kill him. By God's providence David had been brought into Saul's service, and through wise conduct and prolonged hardships he learned to trust God while being prepared to rule Israel.
The tomorrow in the verse was the new moon, a sacred festival celebrated in Israel that fell on the day after David and Jonathan spoke. On that festival both young men were expected to appear with Saul at the meal, but David feared to be present. It was arranged that he should go to Bethlehem to visit his brothers for the sacrifice offered by his father's household and then hide himself in a field not far from the banqueting hall, staying away from the king for three days until the evening of the third day. Jonathan was to observe Saul's response to inquiry about Jesse's son and report it, so that a calm answer of it is well with no angry demonstration would mean David could safely return to court, while rage over the absence would decide that David must flee for his life.