(Excerpt from Chumash Mesoras Harav)
הִשָּׁמֶר לְךָ פֶּן תִּשְׁכַּח אֶת הֹ’ אֱלֹהֶיךָ – Beware that you do not forget the Lord, your God.
The context of the mitzvah of Birkas Hamazon indicates the nature of the mitzvah—the Torah doesn’t require man to thank God; rather, the Torah warns man lest he forget God. The purpose of Birkas Hamazon is to prevent the arrogance which creeps into a man’s heart and causes him to forget that God is the Creator. Fundamentally, Birkas Hamazon is not an act of thanksgiving or praise, but an act of remembering God, a fulfillment of the constant command to remember and be cognizant of our Creator in every aspect of our life. As the Torah concludes this section (verse 18), But you must remember the Lord your God, for it is He that gives you strength to make wealth.
Thus, Birkas Hamazon is not simply a particular commandment regarding food and our satiation; it is instead an expression of the belief and commitment that underpins our entire religious life. Indeed, from the standpoint of the psychology of religion, the telos of Birkas Hamazon, to remember God, is the most important element in one’s religious experience. To oﬀer praise before God is easy; to give thanks, one has merely to become sentimental. However, to remember God and ascribe everything to Him, to attribute the whole cosmic process of creation to God, and to know always that He is the Master, the Lord, and the Owner of everything, requires a mental discipline of the highest order, and it is in truth the basic religious experience. (Lecture on Birkas Hamazon, 1961; Birkon Mesorat Harav, pp. 11-12)