Fact: According to most opinions, nowadays, one should not look at the Kohanim while they are duchening in order to avoid becoming distracted. Furthermore, one should not turn away from the Kohanim while they are reciting the blessing; rather one should face forward and look downwards.
Background: The longstanding tradition of Birkat Kohanim (Priestly Blessing) is rooted in parshat Naso where God commands the Kohanim to bless the Jewish people by reciting a three-part benediction. According to Seder Olam Rabbah, the very first Birkat Kohanim was recited on Rosh Chodesh Nisan, less than a year after the Jews left Egypt; Kohanim have been blessing the Jewish people ever since.
In the Talmud, we find an intriguing statement regarding Birkat Kohanim. The Gemara in Chagigah (16a) cautions that looking at three things can dim a person’s eyesight: a rainbow, a nasi (lit. prince) and the Kohanim when they stood on the duchan (platform in the Temple) and blessed Israel with the Tetragrammaton (ShemHameforash). According to the Talmud, it would seem that only those who witnessed the Priestly Blessing in the Temple (where the Tetragrammaton  was used) were at risk of losing their vision.
This, in fact, is the view of most commentators. Only a small minority, among them Rashi, maintain that nowadays—in the post-Temple period—the Talmud’s warning is still in effect and looking at the Kohanim may result in the dimming of one’s vision.
While losing one’s sight may no longer be a concern, all commentators agree that one should not look at the Kohanim while they duchen. Why the prohibition? According to the Rosh,  this is because of the presence of the Shechinah. The Rosh brings a beautiful midrash  on a verse in Shir HaShirim (2:9) that suggests that irrespective of where and when the Kohanim bless the Jewish people, God’s spirit is present (although God’s presence was more evident during the duchening in the Temple). The verse reads: “There He [God] stands behind our wall, gazing through the window, peering through the lattice. My beloved spoke thus to me.” The midrash comments: “There he stands behind our wall,” behind the walls of synagogues and houses of study; “gazing through the window,” over the priests’ shoulders; “peering through the lattice,” through the priests’ fingers; “My beloved spoke thus to me” and what did He say? May the Lord bless you and protect you (the text of Birkat Kohanim). The Rosh explains that one is forbidden to look at the priests because the Holy One, Blessed Be He, is peering between their fingers, as it says, “Gazing through the window, peering through the lattice.”
This mystical notion of the Shechinah being present during duchening is found in the Zohar as well. The Kaf Hachaim, who, similar to the Rosh rules that one should not look because of the Divine spirit, bases his interpretation on the Zohar.
Taking an entirely different approach, Tosafot explains that looking at the Kohanim during duchening is forbidden because it distracts one from paying attention to the blessing. More recent halachic authorities such as the Beit Yosef and the Magen Avraham agree with the Tosafot. The Magen Avraham, in fact, goes so far as to say that the actual prohibition is not against mere “looking” but against staring since staring can lead to hesech hada'at (a loss of concentration and focus) whereas an occasional glance would not. However, the Magen Avraham concludes that the custom today is not to even glance at the Kohanim since in the Temple, glancing was forbidden. Thus, we refrain from any kind of looking because of zecher l’Churban (in remembrance of the destruction of the Temple).
How then are we to act during Birkat Kohanim? Many worshippers mistakenly turn around even though the Talmud states that a blessing must be given face-to-face. Clearly a widespread misconception in his day as well, the Yaavetz wrote in the 1700s that “one should not do like the amei ha’aretz [the ignoramuses] who turn their backs on the Kohanim because they are afraid of the Talmudic dictum regarding losing vision. There is no blindness of intellect greater than this.” He then goes on to condemn the custom of covering one’s face with a tallit  during duchening, a practice which prevents one from receiving a blessing face-to-face. The proper response is to face in the direction of the Kohanim, look down, and concentrate on the words.
Furthermore, worshippers standing to the side of the Kohanim should be sure to face them rather than the front of the shul.
Finally, we come to the erroneous custom of reciting verses during Birkat Kohanim. Both the Mechaber and the Ramah, basing their ruling on the Talmud, state that it is inappropriate to recite these verses. The Mishnah Berurah likens those who recite the verses to a person who receives a blessing while distracted. In order to avoid losing one’s concentration, one should not learn or engage in any other activity during the Priestly Blessing. The one exception is reciting the prayer to rectify a bad dream, as discussed in Brachot 55b. Tosafotand others opine that reciting this particular prayer is permitted, while according to the Mishnah Berurah and other sefarim even this prayer should only be said during the Kohanim’s melodious song, chanted before the end of each verse. Either way, unlike the recitation of the verses, reciting the prayer to annul a bad dream has halachic sanction.
May we merit to achieve the intimacy with God described by Rav Yehoshua ben Levi (Sotah 38b) in the context of Birkat Kohanim that “Afilu mechitzah shel barzel einah mafseket bein Yisrael l’Avihem shebashamayim” – even an iron curtain cannot separate the people of Israel and their heavenly Father.”
1. Numbers 6:22-23, 27.
2. Ibid., 6:24-26.
3. A chronological work ascribed to the second-century tanna, Yose ben Chalafta.
4. It is recited daily in Israel and by many Sephardim even outside of Israel, and on holidays by Ashkenazim outside of Israel.
5. The Rambam and Shulchan Aruch do not cite the first two in their legal codes.
6. Mishnah Sotah 7:6 lists three differences between the Priestly Blessings that took place in the Temple and those that took place outside of the Temple: 1.The use of the Tetragrammaton 2. In the Temple, the three verses were recited as a single blessing, while outside they were said as three blessings, and 3. In the Temple, the priests (except for the high priest) raised their hands above their heads while outside they raised it to shoulder level. They used to say it as one brachah because in the Temple the response was not “Amen” but “Baruch Shem k’vod malchuto l’olam vaed” (Sotah 40b; Rashi, ibid; Rashi, Ta’anit 16b). [An additional response to the Birkat Kohanim is that recited by the congregation when the chazan recites it in his repetition of the Shemoneh Esrei. That response is “Kein yehi ratzon” (Shulchan Aruch, Orech Chaim 127:2). Amen is only appropriate after a brachah and when the sheliach tzibbur recites it, it is considered a request, not a brachah (Mishnah Berurah 127:10).]
7. Megillah 24b.
8. Pesikta deRav Kahana, parshat haChodesh, 8 (Mandelbaum ed., p. 91).
10. Chagigah 16a.
11. A related custom mentioned by the Rama (Orech Chaim 128:23) is that the Kohanim do not look at their own hands. The Mishnah Berurah 128:90 explains that this is also related to distraction while the Kaf Hachaim (Orech Chaim 128:41) relates it to both distraction and the Divine presence.
12. Sotah 38a, based on Numbers 6:23.
13. See Moshe Hakohen Gross, Nesi’at Kapayim K’hilchatah, 1994, p. 90, note 1 and p. 130 note 14.
14. In this regard, unlike the previous statement, he has many detractors. See also Shulchan Aruch, Orech Chaim 128:23 and Gross p. 131, note 19*.
15. See Gross, p. 134, note 33.
16. Shulchan Aruch, Orech Chaim 128:23.
17. Sotah 39b-40a.
18. Orech Chaim 128:26.
20. See Maharsha (Brachot 55b) who holds that it is only said if one is unsure what the content of the dream was. If one remembers it, they say hatavot chalom. The Chofetz Chaim (Biur Halacha 130) was hesitant about saying this prayer on the second day of Yom Tov because it had just been said the previous day. I have not seen any discussion regarding when the Kohanim recite this prayer.
21. Sotah 40a.
23. There may be differences regarding when and who should say this prayer depending on if the local custom is to duchen daily or only on holidays. For the laws regarding this prayer, see Orech Chaim 130; Gross, Chapter 24 (pages 201-206), and Biur Halachah at the end of Orech Chaim 128.
24. The Aruch haShulchan (Orech Chaim 585:4) mentions another instance of a “pious” reading that in his time often overshadowed the main mitzvah. The custom is to recite Psalm 47 seven times before the blowing of the shofar. The Aruch haShulchan reports that there are those people who do not complete the recitation on time and continue to say it during the actual shofar blasts. This is prohibited. He further states that he is aware of places where the psalm is no longer recited because of this problem.
Reprinted from JEWISH ACTION Magazine, Fall 5762/2001 issue