The Talmud (Brachos 48b) teaches that the first three brachos of birchas hamazon are of Biblical origin based upon the verse, "v'achalta v'savata u'veirachta es Hashem elokecha al ha'aretz hatova asher nossan loch - and you shall eat and you shall be satisfied and you shall bless Hashem, your god, for the good land that he gave you" (Devarim 8:10). The first beracha acknowledges Hashem as the provider of the food. The second beracha expresses our appreciation for the Land of Israel, and for two additional mitzvos that are prerequisites for our retaining the land, bris milah and Torah. The third beracha was originally a beracha thanking Hashem for Yeruhsalayim, the monarchy of Dovid, and the Beis Hamikdash. When the Beis Hamikdash was destroyed this beracha was modified to embody a prayer for the restoration of the monarchy, Yeruhsalayim, and the Beis Hamikdash.
While Ashkenazim generally do not say amen after our own series of berachos, we do recite amen after the third beracha of birkas hamazon - bonei Yerushalayim - to indicate that the three berachos of biblical origin are complete, and to note the addition of the fourth rabbinic blessing. This past Monday we celebrated Tu B'Av, and the Talmud (Taanis 30b, Bava Basra 121b) teaches that one of the causes for celebration was that after the unsuccessful revolt of bar-Kochba the city of Betar fell, hundreds of thousands were killed, and the Romans did not allow the Jews to bury their dead. After several years, Rabban Gamliel and chachmei Yavne prayed and paid significantly until permission was granted for burial. Miraculously, though years had passed, the dead bodies were still fresh and whole. At that time, the rabbis of Yavne instituted the fourth beracha of hatov v'hamaitiv. "Hatov" extolling the goodness of Hashem that the bodies did not decay, and "ha meitiv" - who confers good - referring to the fact that ultimately, they were buried. While this is certainly a noteworthy event, why did Chazal see fit to incorporate it into birkas hamazon? What essential idea is this historical event teaching us to warrant review as often as we eat a meal? The Meshech Chochmo in his commentary on the passuk "v'achalta v'savata" notes that the birkas hamazon contains a great deal more than thanks to Hashem for the sustenance. He sees this prayer as a progression and demonstration of hashgacha pratis throughout our history.
The first beracha was composed by Moshe when the man descended. Every aspect of this nourishment reflected Divine involvement and participation with the people of Israel. The second beracha, composed by Yehoshua, notes not only the Divine conquest of Eretz Yisroel, but also how the land harmoniously interfaces with the divine law and the Jewish nation. The third beracha, authored by Dovid and Shlomo, thanked Hashem for his hashgacha pratis in the mikdash and Yerushalayim (Avos 5:7). Finally, lest one believe that with the destruction of the second beis hamikdash His hashgacha pratis over Klal Yisroel ceased, the miraculous preservation of the myriads of cadavers demonstrated His continuous care and concern for His people even when they are in galus. Hest the beracha has been most inspirational and elevating to the oft crestfallen spirit of the Jewish people during the long diaspora.
Finally, the Jewish people most recently underwent a Tisha B'av and, a few days later, a Shabbos Nahacmu. Where does this extraordinary capacity for resilience come from? The navi Micha proclaims (7:8), "do not rejoice over me, my enemy! Though I have fallen I rise again, though I sit in darkness, the Lord is my light." The Yalkut (567, 568) has two significant comments to share. Firstly, when Hashem punishes other peoples, there is no hesitation to completely wipe out a particular nation. Regarding Egypt the Torah teaches "not one of them survived" (Shemos 14:22). This is not the case with Am Yisroel, where Malachi promises, "for I am Hashem, I have not changed, and you the children of Yaakov, you have not ceased to be" (3:6). In addition, continues the Yalkut, inherent in the very falling of Israel are the seeds for rejuvenation; in the darkness of churban is the light of salvation.
This amazing idea is found in the kinos of Tisha B'av. In kina eighteen there is a reference to the keruvim that the Romans found in the Kodesh Hakodashim. They had the appearance of a boy and girl embracing. The enemy paraded this around Yerushalayim proclaiming that the Jews are involved with idolatry and immorality. In reality, explains, the Bnei Yissochor based on the Talmud (Yoma 54b), Hashem was showing His love for Israel even at the time of destruction.
Birkas Hamazon communicates a great deal more than "thank you Hashem for the food". It has nourished our souls with optimism for almost two thousand years.