 And that mentions rain immediately thereafter indicates that it is appropriate to pray for rain.The Mishnah taught that the absence of one of the two portions of scripture in the mezuzah — and — invalidates the other, and indeed even one imperfect letter can invalidates the whole.The Mishnah taught that the absence of one of the four portions of scripture in the Tefillin — and 11–16 and and — invalidates the others, and indeed even one imperfect letter can invalidate the whole.