R' Joel Rich asked:
> Does anyone know why we say this before shma when we are
> saying it byichidut (& it seems a hefsek) ...

It only appears to be a hefsek if one presumes the previous line to 
be a Birkas Hamitzvah. But if one discounts this possibility, then 
these three words -- which are very on-topic to what we're saying 
before and after it -- are no more problematic than any other piyut 
which is added to that portion of the davening.

Thus, the fact that these three words are accepted as a valid 
practice, is evidence that the previous line is NOT a Birkas 
HaMitzvah.

Alternatively, if one objects to adding piyutim to Birkas Krias 
Shema, then this is just another example of it, and does not need to 
be singled out as being unusual.

Akiva Miller