Genetria is numerology of the Hebrew language and Hebrew alphabet, and is used by its proponents to derive meaning or relative relationship. Several forms can be identified: the "revealed" form and the "mystical form".

The word itself comes from the Greek word 'geometry' and the concept or system is the same as the Greek isopsephy and the Islamic Hisab al-Jumal. Although Hebrew Gematria is the best known now, Greek Gematria predates it by many centuries. There is also a Gematria of Latin-script languages, dating from the early Middle Ages, and very possibly back into Roman times, too. Recent times have also seen an emergence of new gematrias, though these lack a length of exploration that more ancient versions have seen.

Revealed Gematria

The most common form of gematria is used occasionally in the Talmud and Midrash and elaborately by many post-Talmudic commentators. It involves reading words and sentences as numbers, assigning numerical instead of phonetic value to each letter of the Hebrew alphabet. When read as numbers, they can be compared and contrasted with other words. A commentary almost completely dedicated to gematria is Baal ha-Turim by Rabbi Jacob ben Asher.

Gematria is often used by the Maharal of Prague and hasidic Torah commentators (such as the "Sefath Emmeth" from Gur).

One fascinating application of gematria is its use by exegetes to suggest that authors of certain biblical texts were keenly aware of specific mathematical principles and properties. For example, gematria has been employed to contend that the author of Kings, who according to traditionalists is Solomon, was aware of the approximate value of Pi.

Ostensibly, a plain reading of 1 Kings 7:23 indicates that its author believed that 3, rather than 3.14159, is the value of Pi. This tentative conclusion arises from the fact that the verse describes the molten sea that was made in the Temple as being 10 cubits from brim to brim (diameter) and as being encircled completely by a line of 30 cubits (circumference). Since Pi is the ratio of a circle's circumference to the circle's diameter, it would seem that the author of Kings thought Pi had a value of 3, which makes no sense since even a rough measurement would show the difference (1.4 cubits is almost 2.7 feet).

However, gematria may be used to counter the argument that this verse is an example of biblical error. In Jewish tradition, words appearing in portions of the Books of the Prophets are occasionally read (Kri) differently than they are written (Ktiv).

Some biblical scholars, such as Rabbi Judah Loew of Prague of the 16th Century (the Maharal of Prague), trace the provenance of the Kri/Ktiv dichotomy all the way back to the authors of the Books of the Prophets. In its written form (Ktiv), the verse uses the word KAVA (Kuf, Vav, Hey) for the molten sea's circumference. Yet, the word is read (Kri) as KAV (Kuf, Vav).

The numerical value of KAVA is 111 (Kuf = 100, Vav = 6, Hey = 5), while the numerical value of KAV is 106 (Kuf = 100, Vav = 6). 111/106 = 1.047169. If 1.047169 (the value of the Kri divided by the Ktiv) is multiplied by 3 (the value that the author ostensibly attributes to Pi), the result is 3.14151, which closely approximates Pi.

The Vilna Gaon a Rabbinic luminary of the 18th Century known for a remarkable mathematical prowess, is often credited with the discovery of this gematria.

Mystical Gematria

Gematria is a system of recognizing a correspondence between the ten sefirot, or fires of God, and the twenty two letters in the Hebrew alphabet. This system is elaborated in many mystical Jewish writings such as the Zohar.

One example of gematria is that there are twenty-two solid figures that are composed of regular polygons. There are five Platonic solids, four Kepler-Poinsot solids, and thirteen Archimedean solids. Since there are twenty-two letters in the Hebrew alphabet, a correspondence can be inferred between these two disparate categories. The art of gematria is knowing which solid is associated with which letter.

Another example is that of Hebrew numerals. Although there are twenty-two letters, there are twenty-seven numerals necessary to express each number up to 999 (one through nine, ten through ninety, one hundred through nine hundred). The mystical Hebrew numeric system notes that the missing final five letters of the numeral system match exactly with the five 'sofit (word-final) alternate forms of the Hebrew letters.Another use is that words which have the same numerical value, share the same qualities, and reveal still other aspects of the Divine.

Gematria Codes Wikipedia