Siman 201

We hold that the greatest among those at the meal recites the blessing of zimun and Birkat HaMazon (46b), for those reclining are obligated to accord him honor; and even if the greatest arrived at the end of the meal. And if the greatest wishes to give permission to one smaller than him—he may do so, for this is not a lack of honor before him since he himself gives the permission (Bach). And also, this is not included in what they said (55b) that one who is given the opportunity to bless and does not bless, his days are shortened, for the participants did not give him the opportunity to bless. And even though according to the law he must bless, this is because of his honor; and since he waived his honor—his honor is waived, and the law is no longer upon him to bless. On the contrary, this person whom the greatest honored is obligated to bless. And so it appears to me that if the participants honored the greatest—he is forbidden to honor another. However, if the greatest is producing phlegm, which is called "huston"—he may give it to another, because there would be an interruption with a loathsome spitting, and the participants would be disgusted (Magen Avraham).

And it appears to me that all this applies when there is no host present with guests, but rather a gathering where each person eats from his own or at a public mitzvah feast. However, when there is a host and everyone eats from his property—he takes precedence over everyone, since the feast is his. Yet he may honor whomever he wishes. And it appears that it is incumbent upon him to honor the greatest among the diners. And thus our sages, of blessed memory, said (46a): The host breaks the bread and the guest recites the blessing, so that he may bless the host, even if the host is greater than him; and this is for the benefit of the host so that he may bless him. And this is not an obligation upon the host but rather good advice and derech eretz; and if the host waives his blessing and wishes to recite Birkat HaMazon himself—the authority is in his hand. And likewise he may honor whomever he wishes, even if he is not the greatest of the guests. (This is the intention of the Rema at the end of section 1. And the difficulty of the Magen Avraham, small subsection 2, is answered; see there. Examine it and you will find it easy.) And it is obvious that one who pays money for his meal, such as in an inn—is not considered a guest but rather like a host. (Ibid. And that which he wrote that if two are eating..., his words were not clarified to me.)

What is the blessing that the guest recites for the host? "May it be Your will that this host shall not be ashamed in this world, nor humiliated in the World to Come; and may he be very successful in all his possessions, and may his possessions and our possessions be successful and close to the city; and may the Satan not rule over the work of his hands or the work of our hands, and may there not be presented before him or before us any matter of a thought of sin, transgression, or iniquity from now and forever." This is its version in the Gemara (46a). And it is simple that now, when everyone recites Birkat HaMazon, every guest is obligated to recite this blessing even if the host did not honor him with the Birkat HaZimmun. (And perhaps now we do not say at all that the guest blesses, for go after the reason. And examine and you will find it easy.)

It is a simple matter that a kohen precedes everyone, for it is a mitzvah to show him honor, as this is included in "and you shall sanctify him." However, a Yisrael who is a talmid chacham precedes a Kohen Gadol who is an am ha'aretz. The chacham is not required to honor him by way of the law and statute of the priesthood, but the chacham may give him permission to recite the blessing by way of honor. And a kohen who is a talmid chacham, it is a mitzvah to prioritize him. All of this applies when the ba'al habayit is not present. Also, the kohen may show honor to another, and it is not similar to the aliyah to the Sefer Torah, as I wrote in siman 135; see there. A Levi does not have the law of precedence. And one to whom they give the opportunity to recite the blessing and he does not recite it—his days are shortened. This is only when there is a kos shel berakhah (Magen Avraham, subsection 5). And it is a mitzvah to seek that they give him the kos shel berakhah to recite the blessing if he is worthy of it.