The Torah lists Rosh Ĥodesh together with all the other festivals on which we bring musafim (additional offerings) in honor of the day’s sanctity. The Sages derive from Eikha 1:15 that Rosh Ĥodesh is also called a mo’ed (fixed time) like all the other festivals (Pesaĥim 77a). In Temple times, trumpets would be sounded on Rosh Ĥodesh, as it says, "And on your joyous occasions – your fixed times and new moon days, you shall sound the trumpets over your burnt offerings and your sacrifices of well-being" (Bamidbar 10:10).

Because of the sanctity of Rosh Ĥodesh, a custom developed to go out and greet one’s rabbi, similar to the custom on Shabbat to say "Shabbat shalom" to the rabbi (2 Melakhim 4:23, rh 16b, bhl 301:4). There is also a custom to prepare festive meals on Rosh Ĥodesh (cf. 1 Shmuel 20).

The Torah uses a wonderful expression when describing the goat that would be sacrificed on Rosh Ĥodesh, calling it "a sin offering for the Lord" (Bamidbar 28:15). The Talmud (Ĥullin 60b) explains the essence of this matter. In the beginning, God created two great luminaries in the sky, the sun and the moon. The moon, in hopes that God would diminish the sun so that it alone could reign supreme, appealed to the Master of the World: "How can two kings share the same crown?" God, however, said to the moon, "Go and reduce yourself." The moon replied, asking, "Because I made a justified claim before You, I should reduce myself?" God consoled the moon, telling it that the Jews would reckon the months according to its cycle, and that righteous people would be called by its name (i.e., they would use the epithet "the Small" in reference to the moon following its diminution). But the moon was not consoled, so God said, "Bring atonement for Me for making the moon smaller." This is why it says, "And there shall be one goat as a sin offering for the Lord."[1]

This is a very profound concept, but on a simple level, the moon’s reduction symbolizes the deficiencies that exist in creation – the descent of the soul when it arrives in this world and all the failures that man experiences during his lifetime. All these failures and deficiencies are prerequisites for subsequent growth, because coping with hardships helps one reach higher heights in the end, as R. Abahu says, "The wholly righteous cannot stand where penitents stand" (Ber. 34b). In the meantime, though, people commit sins that cause great pain in the world. In order to relieve this pain and repair the flaws, God commanded us to sacrifice a goat as a sin offering. This is the purpose of Rosh Ĥodesh: to show us how a new beginning sprouts from the moon’s reduction, which happened as a result of its sinful indictment of God. Therefore, Rosh Ĥodesh is a good time for new beginnings and repentance; indeed, it is a time of profound joy. However, until the world is redeemed from all its deficiencies, the joy of Rosh Ĥodesh is slightly hidden and is not completely revealed (see also below, sections 15-16).