English: It was taught: It is said here “Shema Yisrael” and it is said there “hasket u-shema Yisrael”; just as there it means attentive silence, so here it means attentive silence — from here that one who reads the Shema must direct his heart.
On the daf / in context: The gezerah shavah establishes that the first verse in particular requires focused intention of the heart for kabbalas ol malchus shamayim.