The Yerushalmi (Brachos 7 3) brings that when Rav Ze’ira honored his student Rav Abba bar Zeminah to make a brachah on the wine and to have in mind to be motzi from the obligation of the brachah, Rav Abba replied to his rebbi: The same way I have in mind to be motzi you with my brachah, you should have in mind to be motzi me in my obligation by answering amen to my brachah.
Why did Rav Abba bar Zemina want to be yotzei with an amen to his brachah?! Isn’t he the mevarech? Why does he need the amen?
The Rema (Darchei Moshe Orach Chaim 167) explains that the reason Rav Abba asked to be yotzei with answering amen is because the obligation of answering amen is also for the mevarech, as answering amen is part of the brachah (Rashi Brachos 47a ad loc. Ad). It is forbidden for a person to answer amen to his own brachah, and therefore, it is an obligation for the mevarech to complete his brachah by hearing amen from the oneh, through the din of “shomea k’oneh.”
However, the Pnei Moshe explained (Yerushalmi ibid ad loc. Amar) that the obligation of answering amen is always incumbent only on the listener, and Rav Abba did not ask to be yotzei with answering amen only because of its virtue. Because after Chazal said (Brachos 57a) that the oneh amen is greater than the mevarech, Rav Abba also wanted to have the merit of answering amen, so he asked Rav Ze’ira that when he answered amen he should have in mind to be motzi him through “shome’a k’oneh.”
