Why does the guest bless his Ba'al HaBait (in Birchat HaMazon) by "Slo Yevosh La'Olam Haze, Ve'Lo Yikalem La'Olam Haba", and not by something more specific which is connected to the meal that the guest just ate now?
Thanks in advance, David Garber.
Good question. Indeed, each and every part of the guest's blessing relates to something that the host did for him. The part of the blessing that you asked about corresponds to the kindness that the host did by happily giving a meal to the guest so that he would not have to embarrass himself and have to rely on charity or on strangers. In return for saving him that embarrassment, the guest gives the host a blessing that he should never experience shame in this world or in the World to Come. (See Sefer Sifsei Chachamim who expounds on this idea.)