Q. Why do we bless the new moon on the Shabbat before each new Hebrew month and what are the origins of this blessing?
A. The ceremony of blessing the New Moon, m’var’chin hachodesh, seems not to have been introduced before the 12th century, though it brings together passages known at least as early as Talmudic times.
There are four sections to the ceremony:
1. Y’hi ratzon – “May it be God’s will”, originally the daily private prayer of Rav (3rd century Babylonia) after the Amidah. Into Rav’s prayer has been inserted a plea to God “to renew this month for us for good and for blessing”. The word chayyim – life, comes 11 times in this paragraph, suggesting the many qualities we hope the new month will bring. Homiletically, the 11 references to chayyim can be linked with the fact that one of the 12 months, i.e. Tishri, is not publicly greeted in this way, but this explanation falls down in leap years when there is an extra Adar and therefore we say the blessing 12, not 11 times.
2. A prayer for our redemption and ingathering, which we hope we will see in the coming month.
3. The actual announcement of the day/s of Rosh Chodesh.
4. A concluding prayer for a month of “life and peace, gladness and joy, salvation and consolation”.
In ancient times the Beth Din in Jerusalem would, after testimony from witnesses who had seen the new moon, officially proclaim Rosh Chodesh and so inform the Jewish world. At first this was done by lighting flares on the mountain tops, and later by despatching messengers (RH, ch. 2). This procedure was replaced in the 4th century by detailed Calendrical calculations worked out by Hillel II.
The old practice, in much altered form, was revived in the Middle Ages when the Rosh Chodesh blessing was introduced. The congregation stands for the ceremony as was done when the ancient Beth Din made its proclamation (Magen Avraham to OH 417:1).
The purpose of the ceremony is to demonstrate that time is a precious Divine boon and every unit of time must be cherished and used wisely.