1 Samuel 20:27

“And it came to pass on the morrow, [which was] the second [day] of the month, etc.] The Targum is, “and it was on the day after it, which was the intercalation of the second month;” when the beginning of the month was judged of by the appearance of the moon, and there was a difficulty about that, what day it appeared on, two days were kept for it; and Abarbinel f420 is clear for it, that two days were kept in this month; but if this was not the case, since the remainder of peace offerings might be eaten the next day, (<030716>Leviticus 7:16). Saul and his guests might meet on the second day for that purpose: that David’s place was empty: on that day also: and Saul said to Jonathan his son;…”

“on the morrow, which was the second day of the month--The time of the moon's appearance being uncertain--whether at midday, in the evening, or at midnight, the festival was extended over two days. Custom, not the law, had introduced this. Saul said unto Jonathan his son, Wherefore cometh not the son of Jesse--The question was asked, as it were, casually, and with as great an air of indifference as he could assume. And Jonathan having replied that David had asked and obtained his permission to attend a family anniversary at Beth-lehem [Act 20:28-29], the pent-up passions of the king burst out in a most violent storm of rage and invective against his son.”

“Son of Jesse - So he calls him in scorn, to note the meanness of his original; and as not deigning to call him by his proper name. To day - For the uncleanness which came by some chance, usually lasted but for one day. 1 Kings (1 Samuel) 20:30”

“Wherefore: Sa1 18:11, Sa1 19:9, Sa1 19:10, Sa1 19:15 the son: Sa1 22:7-9, Sa1 22:13, Sa1 22:14, Sa1 25:10; Isa 11:1, Isa 11:2; Mat 13:55; Pe1 2:4 1 Kings (1 Samuel) 20:28”