Intercalation

The Jewish calendar is based on a lunar month (about 29½ days) and on a solar year (about 365¼ days). Since a solar year is not an exact multiple of the lunar month, it is necessary to add months every so often. Nowadays this is done seven out of every nineteen years on the basis of a calculation, but when the Sanhedrin exists it is their job to decide exactly when to add an extra Adar in order that the festivals should fall in the appropriate seasons.

Rav Natan of Breslav has a fascinating Chasidic perspective on this intercalation.

It has been known since antiquity that the sun is a source of light and that the moon merely reflects the sun's light. By extension, in Chasidic thought the sun is often a symbol for a supernal source of G^dliness, whereas the moon is the symbol for the ability of this world to reflect the Divine light which reaches it from on high. The fact that the moon is completely or partially obscured for part of the month reminds us that at times our physical reality hides itself from holiness, but the power of renewal remains. We pray each month that G^d should repair the "deficiency" of the moon; this corresponds to restoring the world's ability to fully express its potential for good and holiness.

In addition, many Jews who adopt a more mystical approach to mitzvot (mostly Chasidim and Sefaradim) customarily recite a short "intention" before performing mitzvot, stating that they intend to unite two different aspects of G^dliness - precisely those represented by sun and the moon, in order that G^d's indwelling in this world should be united with His lambence. (This is the L'shem Yichud statement found in many prayer books.)(Chasidic thought also discerns worlds of holiness higher than those symbolized by the sun. Nowadays, we would probably symbolize these as the physical processes which enable the sun to radiate.)

Rav Natan explains further that the lack of correspondence between the aspects of sun and moon expresses itself not only in the obscuring of the moon during part of the month, but also in the fact that the sun and moon are not synchronized with each other. Even when the moon fully reflects the light of the sun, there is still a lack of harmony because of the varying cycles. Thus, reconciling the cycles through establishing leap years is also part of the process of uniting the sun and the moon. The moon is deficient not only in its light, but also in its role as time- keeper.

"And this is the deeper significance of the intercalation, that we are commanded to reconcile the year, in order to equalize the twelve lunar months with the solar years in order to fill the deficiency of the moon." By adding months in accordance with the needs of the calendar and of the people, the moon is restored as an effective guide to the seasons.

Rav Natan then goes on to explain why this reconciliation must be done specifically by the Beit Din, whose job is usually to administer justice to earthly litigants.

"Therefore, this is dependent specifically on the Beit Din, for the Beit Din represents the aspect of truth, for they need to judge truth". The "real" truth, according to Rav Natan, is neither the supernal truth of the sun nor the earthly truth of the moon but precisely the appropriate reconciliation of the two. There is no monolithic source of truth; the two aspects must always be present and judgment is always required to reconcile them. So the need for judges to discern truth in a court case is not merely a technical necessity because it is generally difficult to unravel all the facts but rather an existential necessity because the facts are by their nature "out of synch" and require a Torah-based judgment to reconcile.

Based on Likutei Halakhot Dayanim III:11, 12