1 Samuel 20:5

The new moon. The Jews, like many of their surrounding neighbors, observed a lunar calendar, in which the first day of the month began with the evening on which the crescent of the new moon appeared. The first day of the month, called the “new moon,” was a day of special festivities, including offerings (Num. 28:11-15) and the blowing of trumpets over the offerings and sacrifices (Num. 10:10). Such feasts were both tribal and community affairs at this time, and David, as Saul’s son-in-law, would be expected to be present. The narrative does not name the month of the year. However, inasmuch as there also was such a feast at Bethlehem called a “yearly sacrifice” (1 Sam. 20:6), it is possible that this was an annual feast, most probably that of the new year, which came on the first day of the seventh month, Tishri, in the autumn, as it does in the modern Jewish calendar (see p. 108). Such a gathering had been authorized at the central meeting place for all the tribes (Deut. 12:5-16). In the days of Eli this was Shiloh. Later, in the days of the kingdom, it was Jerusalem. After the removal of the ark from Shiloh, it was quite probable that each district held its own gathering. Thus the same kind of feast could have been held in Bethlehem as was held in Gibeah.