[If] one was reading from the Torah and the time arrived for the recital [of the Shema], if he directed his mind [properly], he has discharged his obligation; but if not, he has not discharged his obligation. At junctures [between sections of the Shema or its blessings] one may greet [an-other] out of respect, and he may reply [to a greeting]; but in the middle [of a section] he may greet [another only] out of fear and he may reply. [These are] the words of R’ Meir. R’ Yehudah says: In the middle [of a section] he may greet [another only] out of fear but he may reply out of respect; at junctures [between sections], he may greet [another] out of respect and he may reply with a greeting to any person.