Who knows two hundred thirteen?
Please cite/link your sources, if possible. At some point at least twenty-four hours from now, I will:
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Accept the best answer.
Go on to the next number.
Building on Gershon's answer:
The gematria of the names סיחון עוג is equal to that of כוזו במוכסז כוזו - both 213. The connection: we write these names on the outside of the mezuzah to prevent evil forces (kelipah) from entering the house. Conversely, these two kings were like an "anti-mezuzah" preventing the forces of good (the Jews) from entering Eretz Yisrael, and so they had to be removed first.
כוזו במוכסז כוזו = 213 the words that are written on the back of a Mezuza by the Ashkenazim.
It is also the Gematria of 'וידעו כי אני ה
According to Strong's concordance, there are 213 p'sukim in Tanach in which the word תורה (in its sense of "law" or similar) and 213 in which the word מועד (in its sense of "appointment" or similar) appears. (I have no Jewish source for either of these claims.)