Source for "Beahava" in Birkat Kohanim? What if the Kohen dislikes someone in the congregation?

Question

The Bracha the Kohanim recite for Birkat Kohanim is (Sotah 39a):

אשר קדשנו בקדושתו של אהרן וצונו לברך את עמו ישראל באהבה

who has sanctified us with the sanctity of Aaron and commanded us to bless Your nation Israel with love.

What is the reason for saying the word באהבה (with love), given that the Torah only commands to bless the Jews without explicitly mentioning that it be done "באהבה" (Numbers 6:23):

דַּבֵּ֤ר אֶֽל־אַהֲרֹן֙ וְאֶל־בָּנָ֣יו לֵאמֹ֔ר כֹּ֥ה תְבָרְכ֖וּ אֶת־בְּנֵ֣י יִשְׂרָאֵ֑ל אָמ֖וֹר לָהֶֽם  

 Speak to Aaron and his sons: Thus shall you bless the people of Israel. Say to them:

Additionally, what if the Kohen dislikes one of the congregants, must he not do Birkat Kohanim given that he cannot bless that person "lovingly"?

Answer 1

Indeed, Mishna Berurah (on O"C 128:10) says not to do it in such a case and associates it with the language of the bracha:

כהן שהצבור שונאים אותו או הוא שונא את הצבור, סכנה הוא לכהן אם ישא כפיו (ולכן יצא מביהכ"נ קודם רצה אם אינו יכול לכוף את יצרו ולהסיר השנאה מלבו) וע"ז תקנו בברכה לברך את עמו ישראל באהבה

Magen Avraham (ibid., 11) makes the same association and attributes the rule to Zohar (147b), which reads:

כל כהן דהוא לא רחים לעמא או עמא לא רחמין ליה לא יפרוס ידוי לברכא לעמא דכתיב טוב עין הוא יבורך אל תקרי יבורך אלא יברך

Answer 2

What is the reason for saying the word באהבה (with love), given that the Torah only commands to bless the Jews without explicitly mentioning that it be done "באהבה"

In the sefer Peninei MiShulchan HaGavoah (Parshas Naso, p. 46), it shares the chiddush of Rabbi Aharon Volkin, the author of the Beis Aharon. He quotes a Maharsha on Sotah 38b, which says:

[...] and therefore blessing should only be given to someone who has a good (generous) eye, because the potency of blessing is dependent upon the intention of the one who blesses. This is the meaning of the blessing of the priests who bless the Jewish people "with love" - which means with a generous intention and goodwill. (The host receives this blessing) because he gave of his food with a good will to the poor. He doesn't give inferior bread to the poor but good bread for himself rather he gives the poor of his own bread according to what he has.

Rabbi Aharon Volkin says that this is the reason why the word "with love" is added. Because this is why the Levites were given this task, because they were the only ones that had tremendous Ahavas Yisroel, and in order for a bracha to be complete, the one that blesses, should have good intentions and love for the one to bless.

Answer 3

In order to be zocheh to Kabalas Haschina one has to be b'simcha. A Kohen cannot be b'simcha if he is upset with someone in the Kehillah. So they make the Brocho that Hashem commanded them to be loving toward all Jews and , hence, b'simcha , so they can act as the conduit of blessings from Hashem. As to why that is not included in the Torah, that is because we were dealing with Aharon Hakohen and his sons in Bamidabar 6:23 and we all know that there was no greater Ohev Yisroel than Aharon , and by associations his sons, so it was not necessary to specify B'Ahava. (That is why we cannot look at their hands as the Shechina comes down to rest on their hands if they are zocheh. The 60 words in Birkas Kohanim are also alluded to in Shir Hashirim 3:7-8 which references the 60 "might men" of Shlomo Hamelech. Finally, look at Krias Shma Al Hamittah and you see the posuk from Shir Hashirim said and then the Birkas Kohanim juxtaposed. Same reason. Bring the 60 words of the Blessing and protect for the night).