Question: When the Chazzan or an individual receiving an Aliya to the Torah recites “Barechu Et Hashem Ha’Mevorach” and the congregation replies “Baruch Hashem Ha’Mevorach Le’Olam Va’ed,” must the congregation rise completely or partially or is there no obligation to rise whatsoever?
Answer: The Rama writes in his work Darkei Moshe quoting the Mordechi that it is customary to recite Barechu while standing. This is based on the Talmud Yerushalmi which expounds the verse regarding Eglon, king of Mo’av, “Rise, for Hashem has spoken to you”- Rabbi Elazar understood from here that one must rise while reciting “Amen Yehe Shemeh Rabba” and any other words of holiness.
Based on their words, one must stand while reciting “Baruch Hashem Ha’Mevorach Le’Olam Va’ed,” for even Eglon, king of Mo’av, stood when he was told the word of Hashem. It is therefore compulsory to stand while answering Amen to Kaddish and while reciting “Baruch Hashem Ha’Mevorach”. Many other great Acharonim, including the great Mekubal, Rabbeinu Menachem Azarya of Pano, rule likewise.
On the other hand, Rabbeinu Chaim Vital, chief disciple of the saintly Ari z”l, writes that the great Ari z”l would not stand up while answering Amen to Kaddish and he said that the Yerushalmi quoted by the Rama is incorrect, for it is a mistaken passage erroneously printed in the Talmud Yerushalmi. Only when the Ari was already standing and the Chazzan began reciting Kaddish would he remain standing until the conclusion of the Kaddish at which point he would be seated again. Indeed, the Rama writes in the beginning of the aforementioned Darkei Moshe that the Maharil would not stand during Kaddish of the recitation of “Baruch Hashem Ha’Mevorach Le’Olam Va’ed.” Only if he was standing in any case and the Chazzan began Kaddish would the Maharil remain standing until the conclusion of the Kaddish.
Based on this, according to the opinion of the saintly Ari z”l, there is no need to stand during Kaddish or during the recitation of “Baruch Hashem Ha’Mevorach Le’Olam Va’ed.” Maran Ha’Chida writes that were the great Rabbeinu Menachem Azarya of Pano to have seen the words of the holy Ari, he would certainly have agreed that one may remain seated during Kaddish, for Rabbeinu Menachem Azarya ruled mostly based on the words of the holy Ari.
The great Rabbeinu Yosef Haim of Baghdad writes in his Sefer Od Yosef Hai that the custom in his hometown of Bagdad is that the congregation rises slightly while reciting “Baruch Hashem Ha’Mevorach Le’Olam Va’ed”; he writes that he searched for a source for this custom but he has not found one. This is indeed the custom is several places today. However, there is no basis for this custom, for according to the Ashkenazi custom which follows the Rama, one must be standing completely while reciting “Baruch Hashem Ha’Mevorach” whereas according to the Sephardic custom, there is no need whatsoever to standing while reciting “Baruch Hashem Ha’Mevorach.” All Sephardic Acharonim agree with the ruling of the Ari z”l that there is no need to stand during Kaddish or Barechu.
Summary: The Ashkenazi custom is to rise for answering Kaddish and reciting “Baruch Hashem Ha’Mevorach Le’Olam Va’ed.” According to the Sephardic custom, however, there is no need to stand during Kaddish and Barechu. Nevertheless, even according to the Sephardic custom, if one was already standing and the Chazzan begins reciting Kaddish, one should not be seated until the Chazzan concludes the Kaddish. If a Sephardic individual is praying in an Ashkenazi synagogue, it is preferable for him to stand during Kaddish and Barechu in order not to be the only one sitting while everyone else around him stands.