The Zohar, in explaining the importance of the new moon and our celebration of its renewal each month, states: "The Jewish nation is compared to the moon. Just as the moon wanes and seems to disappear into darkness only to be reborn, so too the Jewish people often appear to be overwhelmed by the forces of darkness, only to reemerge as a nation reborn."

The main religious teaching of Rosh Chodesh, once observed as a semi-festival and even nowadays distinguished by its festive liturgy, is its concept of renewal. Each new moon marks a new beginning both for the individual Jew and for the Jewish people as a whole. Even the word for month (chodesh) is connected with the word new (chadash) and suggests beginning afresh. Similarly, the date in every marriage contract (Ketubah) is given in Hebrew, although the document is in Aramaic, in order that the word chodesh be used to indicate that for the newly married couple their wedding is the beginning of a new life.

In addition to its being a holiday as the beginning of a natural division in time, Rosh Chodesh was also regarded as a day of penitence because a sin-offering was one of the sacrifices brought on it (Numbers 28:15). Moreover, the diminution of the moon's light was regarded as symbolic of human guilt, and the reappearance of the moon was regarded as a sign of atonement calling for celebration. Even today, the eve of the New Moon is called "the minor Day of Atonement" (Yom Kippur katan), and is observed by some pious Jews as a fast day with the recital of penitential prayers (selichot) and confessions of sins at the afternoon service for the sins of the preceding month.

The combination of joy and solemnity on Rosh Chodesh is not at all inappropriate. The beginning of a new period in time is an obvious occasion when a person should take stock of his life and, since no one is sinless, is an appropriate time for improvement.

Corresponding to the renewal which takes place on the New Moon in nature, Rosh Chodesh can be a time for renewal in man's spiritual life. Like Rosh Hashana (the first day of which is also Rosh Chodesh) the new moon should make man conscious of the rapid flight of time, and it may impel him to use his limited time on earth wisely. By the use he makes of his time a man is to some extent its master. Thus, through the impetus that Rosh Chodesh gives to atonement it becomes a day of joy.

The moon has an even deeper symbolical significance in Jewish thought. The rabbis suggest that the Jewish people are comparable to the moon and that other nations are comparable to the sun. The great nations of the ancient world, much more powerful than Israel, arose like the sun to full brilliance, but after a while they disappeared from the world scene. The Jewish people, never as great as other nations, have nevertheless outlived mighty empires. Like the moon, the Jews have undergone many phases of persecution without being destroyed, and, phoenix-like, they have renewed themselves out of the ashes. The continued existence of the Jewish people is a phenomenon that cannot be explained rationally and even secularist thinkers have described it as something mysterious.