Gemara:

Rosh Hashana 

Halacha:

Tefillah 

Collections: R' Grunstein Shir Shel Yom at Mincha

References: Rosh Hashana: 31A  

Description

When we just remember and reanact what was in the times of the Temple, there's no need to MIMICK exactly what they did but just to remember it. Thus, we say Shir Shel Yom once a day and not twice (as they did in the Temple) just like at the Seder, we don't eat a peice of meat at כורך even though, in the time of the temple, Hillel's sandwhich consisted of both (Korban Pesach) meat, marror and Matza.