In order to prevent hatred and insult, the Sages permitted offering greetings in the middle of reciting Shema and its berakhot to one to whom courtesy demands doing so. The poskim write that since it is accepted nowadays not to interrupt in the middle of prayer, honorable people are not insulted when they are not greeted and asked how they are. Therefore, no permission is granted to interrupt in the middle of Shema and its berakhot in order to address an honorable or revered person (MB 66:2, based on Sefer Ha-ĥinukh). However, if someone who does not understand the value of prayer approaches the woman praying, and if not answering will likely cause insult, it is permitted to initiate a greeting. Similarly, a newly religious person whose parents do not understand the value of prayer may greet them succinctly. In the middle of the verses “Shema Yisrael” and “Barukh Shem” one must not interrupt, unless a life is at stake.
One may interrupt by talking in the middle of Shema and its berakhot in order to save herself from bodily harm or monetary loss, although it is preferable, if possible, to finish the paragraph or berakha she is reciting before doing so (see BHL 66:1).
One who sees her friend committing a sin should hint to her in order to prevent her from sinning. However, if her friend does not take the hint, she must interrupt Keri’at Shema and its berakhot to tell her to separate from the prohibition, for if the Sages permitted the interruption of Keri’at Shema and its berakhot for the honor of a human being, one may certainly interrupt for God’s honor (Ritva, Kaf Ha-Ĥayim 66:7).
One may interrupt in the middle of Birkhot Keri’at Shema to respond to Kaddish, Kedusha, and other sacred words. These laws will be addressed outlined below (20:9-10).