Halacha:

Shabbat,  Tefillah 

Machshava:

Shabbat,  Tefillah 

Description

We add many additions to the morning Shabbat Shacharit service, and yet one stands out- לא-ל אשר שבת of which the RAMA paskens that if you didn't say it, you have to repeat it [in counter distinction to ALL other additions]. Why is this passage so essential to the Shabbat experience?