Birkat kohanim- ברכת כהנים is a mitvah. Why don’t we observe it? TB Sotah 38ff

 The Gemara is quite clear that the priest bless the congregation with the priestly benediction (birkat kohanim- ברכת כהנים) every day. It’s a mitzvah. The Shulkhan Arukh’s chapter 128 with its 45 paragraphs delineates what is the correct procedure for a Kohen to bless the congregation. To this day, the Sephardim still have the kohanim ascend and blessed the congregation. It’s a great mystery why the Ashkenazic Jews dropped this mitzvah of the daily birkat kohanim. Ashkenazic Orthodox synagogues the kohanim bless the congregation with birkat kohanim only during the holiday Musaf service. 

The Vilna Gaon wanted to revive the custom of the daily birkat kohanim amongst the Ashkenazi communities based on our Gemara, TB Sotah 38ff. His attempt failed and we Ashkenazi Jews in the diaspora still do not have the kohanim bless the congregation on a daily basis. Nevertheless, his students who made Aliyah to Israel, instituted the custom of the daily birkat kohanim there. Now everybody in Israel calls upon the kohanim to bless them with the birkat kohanim.

 The Rama gives his explanation why we observe this custom only on holidays.

“The custom in these lands is that they only perform the priestly blessing on Yom Tov since then they are in a joyous state due to the Yom Tov, and "a good heart is the one that blesses". As opposed to other days, even Shabbat during the year where people are distracted by thoughts of their livelihood and missing work. And even on Yom Tov, they only perform the priestly blessing during the Mussaf service, for [immediately after] they leave the synagogue and are joyous due to Yom Tov. [His own opinion]. And every Shachrit and Mussaf prayer service where they do not perform the priestly blessing, the prayer leader says "Our God, and the God of our forefathers...", like was mentioned above at the end of siman 127. And they perform the priestly blessing on Yom Kippur just like on Yom Tov. And there are places where they perform the blessing during Ne'ilah; and there are places where they do even in Shachrit....” (Shulkhan Aruch, Orekh Hayim, 128:44)

 Is he really saying that the priestly benediction can only said when we have a joyous heart and the only time we really have a joyous heart is when the holiday services are almost over and were ready to go home for the Festival meal?!

I find standing face-to-face with the kohanim when they are blessing the congregation very moving. It’s a shame that liberal congregations have dropped this mitzvah completely.