...no less and no more... The reason why there are twenty-two is rooted in the first foundation, into which it is forbidden to inquire, as discussed earlier (Opening 15). For these are the levels required for the intended purpose …in order to give the lights the power to act… so that the lights prepared in the Sefirot can produce their requisite effects, as will be discussed further below.
The letters are different combinations of Kindness, Judgment and Mercy – lines and dots, signifying opening and closure.