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, or beginning of each month, was celebrated with especial sacrifices and blowing of trumpets (marginal references.) The feast was kept with great solemnity as “a day of gladness,” and we may presume that the “peace offerings” offered on the occasion furnished the tables of those that offered.