To-morrow is the new moon - The months of the Hebrews were lunar months, and they reckoned from new moon to new moon. And as their other feasts, particularly the passover, were reckoned according to this, they were very scrupulous in observing the first appearance of each new moon. On these new moons they offered sacrifices, and had a feast; as we learn from Numbers 10:10; Numbers 28:11. And we may suppose that the families, on such occasions, sacrificed and feasted together. To this David seems to refer; but the gathering together all the families of a whole tribe seems to have taken place only once in the year. There is a yearly sacrifice there for all the family, 1 Samuel 20:6.

the new moon The months of the Hebrew were lunar months, and they reckoned from one new moon to another: and, as their feasts, particularly the passover, were reckoned according to this, they were very scrupulous in observing the first appearance of each new moon. On these new moons, they offered sacrifices, and feasted together: but the gathering together of all the families of a tribe on such occasions seems to have taken place only once in the year.

1 Samuel 20:6 If your father at all miss me, then say, David earnestly asked leave of me that he might run to Bethlehem his city...

Numbers 10:10 Also in the day of your gladness, and in your solemn days, and in the beginnings of your months...

Numbers 28:11 And in the beginnings of your months you shall offer a burnt offering to the LORD; two young bullocks, and one ram...

2 Kings 4:23 And he said, Why will you go to him to day? it is neither new moon, nor sabbath. And she said, It shall be well.

Psalm 81:3 Blow up the trumpet in the new moon, in the time appointed, on our solemn feast day.

Colossians 2:16 Let no man therefore judge you in meat, or in drink, or in respect of an holy day, or of the new moon, or of the sabbath days:

that I may

1 Samuel 20:19 And when you have stayed three days, then you shall go down quickly...

1 Samuel 19:2 But Jonathan Saul's son delighted much in David: and Jonathan told David, saying, Saul my father seeks to kill you: now therefore...

Psalm 55:12 For it was not an enemy that reproached me; then I could have borne it...

Proverbs 22:3 A prudent man foresees the evil, and hides himself: but the simple pass on, and are punished.

John 8:59 Then took they up stones to cast at him: but Jesus hid himself, and went out of the temple, going through the middle of them...

Acts 17:14 And then immediately the brothers sent away Paul to go as it were to the sea: but Silas and Timotheus stayed there still.

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