"PEERING THROUGH THE LATTICES"
Shir HaShirim (Song of Songs) Rabbah 2:9 provides the thought behind the spreading of the kohanim's fingers while performing the blessing:
"My beloved is like a gazelle or the fawn of a deer, behold, he stands behind our wall looking through the windows, peering through the lattices. My beloved raised his voice and said to me, 'Arise, my beloved, my fair one, and come away." (Song of Songs 2:9-10). Behold, he stands behind our wall. G-d is standing, so to speak, behind the walls of the synagogues and study halls. Looking through the windows, meaning G-d is looking through the space between the shoulders of the kohanim when they stand together pronouncing the priestly blessing. Peering through the lattices. Meaning, God is peering through the space between the fingers of the kohanim when they raise their hands to bless the people.
It is customary for the congregants to avert their eyes and not look directly at the kohanim while they perform the blessing, so as not to make direct eye contact with the Shechinah, the light of HaShem's presence that shines forth from between the spread fingers of the kohanim. Likewise the kohanim also do not look at their fingers which are covered by their spread tallitot (prayer shawls).
The chazan (prayer leader) sings aloud, word for word, birkat kohanim, and the kohanim repeat after him, word for word. After each of the three blessings the congregation answers "amen." At the conclusion of the blessing, as the chazan proceeds with the prayer service, the kohanim say to themselves, "Look down from Your holy Heavenly Abode and bless Your people and the Land which You have given us…"
"SIXTY MIGHTY MEN"
Birkat kohanim in Hebrew, consists of a total of fifteen words, three in the first blessing, five in the second and seven in the third blessing. Furthermore the total number of letters in the blessing is sixty. This recalls the verses from the Song of Songs 3:6-7:
"Behold the litter of Solomon; sixty mighty men are around it, of the mighty men of Israel. They all hold the sword, skilled in warfare; each one with his sword on his thigh because of fear at night." Just as sixty armed guards watched over and protected King Solomon, so do the sixty letters of the priestly blessing guard over and keep us from harm. Likewise there is a custom for someone who experienced a disturbing dream in the night to silently recite a request while listening to the priestly blessing, that their dream bear a positive message and not an ominous message.
"So that I will bless them." The blessing is from HaShem. The kohanim are merely the vehicles by which the blessing is transmitted to the people.
As noted above, before making the blessing the kohanim first say "Blessed are You, HaShem our G-d, Sovereign of all, Who has sanctified us with the sanctity of Aharon and commanded us to bless His people Israel with love." It is incumbent upon the kohanim to love their brethren. A kohen who harbors animosity to anyone in the congregation must not participate in the blessing.
AN ANCIENT FIND
In 1979 archaeologist Gabriel Barkai discovered an ancient scroll dating back to the first Temple period, which contained the priestly blessing. The discovery was made just outside of Jerusalem’s old city. It is the oldest scroll yet discovered containing text from the Torah.
IDENTIFYING THE GRAVE OF A KOHEN
Many kohanim have inscribed on their graves a depiction of two hands performing the priestly blessing. Anyone who sees the grave knows immediately that the person resting below it was a kohen.
This illustration depicts the Priestly Blessing in the Holy Temple. The blessing recited here differs in several respects from the Priestly Blessing recited outside the Temple. As the Mishna (Tamid 7:2) describes, the kohanim “went and stood on the steps of the Ulam (in the drawing they are seen standing on the top step). The first set [the five who had entered with the utensils for lighting the lamps and cleaning the incense altar] now stood to the south of their brother kohanim (in the center of the drawing and south of the steps), holding the five utensils… They recited the Priestly Blessing as a single benediction, and not three (as it is recited outside the Temple) … In the Temple the kohanim raised their hands above their heads, except for the Kohen Gadol (High Priest) (seen on the left), who did not raise his hands above the tzitz.” In this picture, the kohanim are seen raising their hands as high as their heads, in accordance with Targum Yonatan to Leviticus 9:22.