tefilla - Minhag to pause in middle of birkas kriyas shema

Many (if not all) shuls that I have been to have it such that in the first bracha of kriyas shema everyone reads until

וכלם פותחים את פיהם בקדשה ובטהרה, בשירה ובזמרה, ומברכים ומשבחים ומפארים ומעריצים ומקדישים וממליכים

The shliach tzibbur then reads this line, then everyone continues with the words

את שם האל המלך הגדול הגבור והנורא קדוש הוא

What's awkward is everyone is stopping in the middle of a sentence. My question is two fold

1. I've noticed many siddurim break up the paragraphs, showing justification for this pause. What came first, the minhag to pause? Or the siddur had this break first, causing the minhag to develop. I guess looking at an old siddur will help


2. Regardless how it started, what is the purpose for this pause (I'm assuming it's not arbitrary)? It seems inappropriate to pause in the middle of a sentence