God commands no observance of the new moons in either Testament; He only adds special sacrifices and trumpet blowing (Numbers 28:11-15; 10:10), which set the day apart from common days but do not make it a holy day. The one exception is the Feast of Trumpets, which falls on the new moon of Tishri. Israel added to God's word by feasting, abstaining from work, and refusing to buy and sell on new moons (I Samuel 20; Amos 8:5-6). Feasting was a social custom, perhaps growing out of family thank offerings. God does not condemn it, but He did not command it, and Deuteronomy 12:32 and Proverbs 30:6 warn against adding to His word. When Israel's zeal produced hollow formalism and injustice, God said He hated their new moons (Isaiah 1:14). The new moons mark time. Because the festivals of Leviticus 23 fall on fixed dates that must be calculated from a new moon, they keep God's people on track with His plan. Colossians 2:16 suggests the early church observed them in some way, but the sacrifices typify Christ's work and are no longer required (Hebrews 5-10). Without a direct command, the new moons are best treated as a tool, much like the preparation day before the weekly Sabbath. At the least, a Christian should carefully mark their passing. They might also serve as a time for the spiritual sacrifice of praise and thanks (Hebrews 13:15-16), without becoming ritual. Any custom of keeping them is human, not God's.

The first month, Abib, begins with the new moon that coincides with the green ear stage of barley in early spring. The earliest reckoning likely relied on visual observation of the new moon. The ancient Israelites, being closely tied to nature's cycles, could tell by examining the local barley crop whether the ears would reach the green stage by the next new moon. If they would, that new moon began Abib. If not, the month was postponed, and the following new moon began Abib. Later, the Israelites, most likely the Levites who were in charge of the calendar, developed a system for calculating the appearance of new moons with great accuracy. Their calculations rested on astronomical data collected over many hundreds of years, and they could eventually predict the conjunction of moon and sun to the minute. Visual sightings verified the calculations, and the high priest sanctified the new moon for the nation, pronouncing it valid and set apart for determining God's appointed times, the holy days. The new moon of Tishri, the seventh month, may also have been treated as a New Year, but the biblical phrases cited for this can be explained otherwise. God's plain statement in Exodus 12:2 establishes Abib 1 as the beginning of the year.