During the cantor's Repetition of the Amidah, the kohen or Kohanim remove their shoes. The shoe removal prevents the congregation from snickering at a kohen who happens to have a torn shoe lace and remains behind to tie his shoes and refrains from joining his Kohen brethren. The shoes are stowed beneath a table or chair, out of respect for the synagogue. They then file to the nearest sink, where the local Levi performs the washing-the-hands ritual, pouring water from a large cup over the kohen’s hands six times to heighten his holiness. (Water is a spiritual vitamin.)

The kohanim then proceed to stand at the eastern side of the synagogue, which in most synagogues is the platform at the front, directly in front of the Aron. The people stay in their places, gather their children near them, and cover them all with their Tallit. Facing east, the kohanim cover their heads with their taleitim, and at the verbal signal “Kohanim!” from the cantor, they turn counterclockwise to face west, out over the congregation, and recite the blessing said before Birkat Kohanim. They then extend their arms to full length and raise them to shoulder height, with the right hand slightly higher than the left, and with each hand forming a kind of W—pinky and ring fingers together, middle and pointer fingers together, and thumbs touching at the first joint, thus forming three spaces.

...the hands of the kohen become symbolic of the Western Wall, one of the places the Shechinah (Divine Presence) is found...

2. The original Vulcan Hand Sign

Where do you think Mr. Spock got the idea? Little Leonard Nimoy found himself in Shul often, where he would peek out from under his father’s tallit and noticed the unusual hand positions assumed by the kohanim as they delivered the Priestly Blessing. When he grew up and became an alien, he adopted the split-finger posture and Vulcanized it. However, the real reason for the posture is that during the Priestly Blessing, the Shechinah hovers above the kohen’s head, while the hands of the kohen become symbolic of the Western Wall, one of the places the Shechinah (Divine Presence) is found. Just as the Shechinah “peers through the cracks” of the Western Wall, so to speak, seeking an outlet for its presence, so too does the Shechinah seek a “crack” during Birkat Kohanim through which to connect to the congregation. Towards this end, the kohen forms five spaces between his fingers to symbolize cracks.

3. Don’t Worry, Be Happy

To bless someone else one, the kohen must be in a buoyant state of mind himself - which is why this ceremony is reserved for the holidays in so many communities¹ . Rosh Hashanah, Yom Kippur, Sukkot, Shmini Atzeret, Simchat Torah, Pesach and Shavuot all see the kohanim get up to do their thing. And that’s also why Birkat Kohanim is recited during Musaf: because Musaf is the last part of the services, and Halachah knows that we’re only human and get tired after sitting in shul for a while, and get excited when it comes time to go home. Thus, as services come to an end, we get happier, and when you’re happy, well… when’s a better time to say Birkat Kohanim than when you’re happy?