- In the blessing that begins with the words “Have mercy” and concludes with “Who rebuilds Jerusalem,” we mention the monarchy of the house of David because it was through David that Jerusalem was sanctified. There therefore cannot be any complete consolation until the monarchy of the house of David is restored to its original status. (Shulchan Aruch OC 187 with Mishnah Berura)
2. Consequently, one who omits mentioning the house of David must return to the beginning of Bircas Hamazon. (ibid.)