Why when a holiday falls on a Shabbat, do we say an abridged version of the Birkat Kohanim when on weekdays we do the entire thing?
From Asher M.

Great question.

The basic reason is that on Shabbat we should not pray for specific needs and
the additional prayers associated with Birkat Kohanim contains just such
prayers. The Pinei Menachem cites one reason for this prohibition is that on
Shabbat we do not supplicate HaShem for mundane matters such as sustenance, one
of the main themes of the last supplication at the end of Birkat Kohanim. In
contrast, the Alter Gerer Rebbe remarked that it is permitted for one to cry on
Shabbat for the purpose of repentance. He cited as proof to this halacha that we

find that removing the covering of the heart is referred to as milah,
circumcision, and the mitzvah of milah, circumcising a male child on the eighth
day overrides the prohibitions of Shabbat. Thus, removing the covering of the
heart, i.e. repentance, is also permitted on Shabbat.

Aaron Parry