In last week’s section we saw that there is a Mitzvah for the Kohanim to bless Am Yisrael. When a Kohen who is fit to give a blessing does not partake in the blessing, he may be nullifying the Mitzvah which would be viewed as a negation of three commandments. Refraining from giving a blessing is perceived as nullifying three mitzvot based on the pesukim: “ko tevarchu” – so you shall bless, “amor lahem” – say to them and “vesamu et shemi” – and they shall place my name. These three statements, though incorporated as part of the mitzvah of Birkat Kohanim, are understood as three independent commands (See Sota 38b, Rambam Hilchot Tefila ch.15 halacha 12). Yet, at certain times, not partaking in the blessing is not viewed as a non-fulfillment of the mitzvah. At other times, a kohen may not be required to bless, though if he does, he is considered to have fulfilled a mitzvah.
Ideally, the Torah teaches us, “Amor lahem”- “say (call) to them”. The beracha should be recited where there is a “them”, at least two Kohanim, who are called upon to recite the beracha. Since it is the call to the Kohanim which applies the “chiyuv”, requirement to recite the beracha, should a Kohen not be present in the synagogue when the Kohanim are called upon to bless he is exempt from reciting the beracha.
When a Kohen has recited the Birkat Kohanim at least once during the day he is exempt from reciting it again that same day. In halacha we distinguish between a “chiyuv”, requirement to fulfill a mitzvah, and a “Kiyum”, a fulfillment of the mitzvah. Though, a Kohen who has recited the beracha once during the day is exempt from repeating it again, if he chooses to repeat the blessing he is viewed as fulfilling a mitzvah. Many poskim see this as analogous to the mitzvah of tefilin. The basic requirement is to put on tefilin once a day. Yet if one wears his tefilin all day (as was the custom in the Tanaik and Amoraik period), he is viewed as continually fulfilling that mitzvah.
We have pointed out that the “chiyuv” requirement of Birkat Kohanim applies when there are two Kohanim as well as a calling out to them to bless. In the event that one is not present at the time the Kohanim are called to give the blessing, there is no “chiyuv”. So too, if there are not two Kohanim present there is no “chiyuv” to bless. Therefore, if there is only one Kohen present he is not “chayav”- required to recite the beracha. If he chooses, nonetheless, to proceed and recite the beracha, he is “mekayem”-fulfilling the mitzvah. For this reason, when there is only one Kohen who stands up to recite the Birkat Kohanim, we do not call out “Kohanim”, but rather, the Kohen begins with the blessing as soon as the Sheliach Tzibur completes birkat Modim of chazarat hashatz (See Sota 38a).
When there is a “chiyuv”-a requirement to bless the Birkat Kohanim, a Kohen who refrains from doing so is perceived to have nullified three “chiyuvim”. At other times, reciting the beracha is not a “chiyuv” at all and a Kohen may choose to refrain from reciting the blessing. In certain situations even though there is no “chiyuv” there is a “kiyum” fulfillment if the beracha is recited.