Halakha Yeremia 10:10: Mishneh Torah, Foundations, Mishneh Torah, Reading the Shema, Kitzur Shulchan Arukh & Tur

This is as the prophet says: "But the Lord God is the true God" (Jer. 10.10); He alone is the Truth, and no other being possesses a truth similar to His Truth, even as the Torah says: "There is none other like unto Him" (Deut. 4.35), meaning, there is no other true being, besides Him, like unto Him.

The divisions between the sections are as follows: Between the first blessing and the second; between the second blessing and the Shema; between the first section and second section of the Shema; between the second and third section of the Shema. One reading the Shema, when reaching these places, greets one whom it is his duty to honour, and acknowledges the greeting of anyone who first salutes him. But the conclusion of the third section and the opening words of the subsequent blessing are regarded as the middle of a section. One may only pause there either to salute a person of whom one stands in awe or to return the greetings of a person whom it is one's duty to honour.

The rule we stated [above] —that it is permitted to interrupt in mid-section for those things which we enumerated above does not apply to the verse: Shema Yisrael etc. and: Baruch sheim kevod malchuso le'olam va'ed, because when reciting these two verses it is prohibited to interrupt in any circumstance. Even if the king greets you, you may not interrupt to respond. Between Ani Hashem Elokeichem and Emes veyatziv you should also not interrupt because Scripture states:¹³Jeremiah 10:10. "And Adono-y Elohi-m is true." Therefore, [to fulfill this verse], it is not permitted to interrupt between elokeichem and emes. It is preferable to take care not to interrupt until after you have also said the word veyatziv (because it also means "truth.") Afterwards after having said emes veyatziv you may interrupt just as any other place in mid-section. (The practice of greeting or responding to a greeting nowadays is not insisted upon and you should not interrupt for this purpose even [when you are] between sections.)¹⁴Although the Talmud allows for this interruption in various situations.