Minhag to pause in middle of birkas kriyas shema

Question

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

Answer 1

The Tur (OC 61) says, in his guidance on careful pronunciation of Hebrew, to be careful to pause between a word ending in a ם and a word starting with an א, and one of the examples of that that he mentions is here וממליכים את. There's no need for a big pause or a paragraph break anymore than at the other places he mentions (such as שבחי ירושלים את or וראיתם אותו). Here and here are old Siddurim with no paragraph break there.

Perhaps people became extra careful at this location in particular because slurring the words can make the את sound like מת which in this case is awfully heretical.

Answer 2

I was shown the Chasam Sofer (Gloss to Orach Chaim 59:3) brings the Tur @DoubleAA mentioned as the source for the custom, and adds that we apply it at this point in the prayers because if we were to slur our words, it would sound like וממליך מת, corronating the dead. Since there are indeed those who worship the dead, we ought to be extra careful to avoid this phrase.

The Siddur Tzelusah D'Avraham has a commentary on the Siddur called "Emek Bracha". This Siddur is based on the practices of Rav Avraham Landau (1784 - 1875) and it was put together by his grandson Rav Menachem Mendel Chaim Landau. It writes as follows:

וממליכין את שם העולם נהגו להפסיק בין וממליכין לאת שם ולהמתין על הש"ץ והוא על פי הטור שכתב בסימן ס"א שלא לתכוף וממליכין את שם עיי"ש והטעם כדי שיהיו כל הקהל עונין כאחת את שם האל הגדול כו' והא דרך שירה וכמו הקדושה עצמה

We crown the name. People are accustomed to pause between "וממליכין" and "את שם", and to wait until the prayer leader. This is based on the Tur (OC 61) not to be too quick to say וממליכין and את שם. And [another] reason is so the whole congregation says together "The Great Name etc." This is in the manner of a song of praise, like Kedushah.

So, besides attributing the reason to the Tur, as @DoubleAA suggested, he adds that there's an element of "song" to this custom.

Like DoubleAA, I noticed many older siddurim don't have a paragraph break. Many had a period or colon before את שם, probably in deference to people pausing. We need more evidence how old this custom is, to compare to how siddurim print this line. From the above source, it's at least approximately 100-150 years old.

What's ironic is this siddur is nusach Sefard, so they say וממליכין, making it a little less problematic to say the word את immediately after. Maybe that's why he suggests another reasoning.