ברכת המזון

(undefined) To recite the blessings after meals, as it is stated "and you will eat, and you will be satisfied and you will bless the L-RD your G-D" (Deuteronomy, 8:10)

Meaning, Birkat Hamazon. Similarly, we must also bless before Him as it says "You shall eat, and be satisfied, and bless." For it is forbidden for a person to benefit from this world without a blessing, as it says "Hashem's is the world and everything in it." But after you have said a blessing, it is considered that it belongs to you, as it says, "And the earth, He has given to mankind"...

According to the simple explanation, this is not a commandment, rather a fact that the goodness of Israel will be so great that you on your own will recognize Hashem's kindness and be inspired to bless Him. And after this, the Torah warns us to guard ourselves from forgetting that this is all from Hashem, since the nature of man is that when great goodness comes to him, he will bless Hashem, but then afterward as the days pass he will take the goodness for granted, and he will forget how things were before.

To bless Hashem after eating grains - to bless Hashem after man eats and is satisfied from bread or from the seven species mentioned in the text (Devarim 8:8). And those he is satisfied from and regular bread consists of bread made from wheat and barley, and rye, oats and spelt are included as well....

The reason for the mitzvah: As an introduction, haven't I told you, my son, previously that Hashem has all the glory and honor and goodness and wisdom and ability in the world even without us blessing Him, and the words of a human and all of his actions whether good or bad will neither add nor take away from Hashem. Therefore, we need to understand that by saying "Blessed are you, Hashem" we don't mean this literally, as if we are adding a bracha on to the One who needs no additions G-d forbit, since He is the master of everything and of all the blessings...

...This acknowledgment inspires us in our souls through our words to understand that He is the One who blesses, and this includes all the blessings. And from this inspiration of goodness in our souls and the focus of our thoughts we will thank Him for all the goodness included in Him, and that He is the king over all of it, to send the goodness to whomever He wishes, and then we will be worthy in this good action to continue to receive His blessings.