“The blessing of the Torah” means that the body obligates him to bless. That is, the body that the Creator created with a nature that if he receives something good from someone, he blesses him, and this is called “the blessing of the food” from the Torah.
“Is not commanded” means that the body does not obligate him to bless because he feels he needs a few more things that the other one could give him but is not giving him. At that time, the body says that it is still not satisfied with Him and cannot say that He is good and does good, since I still need a few things so why is He not giving me? And yet, he is strict with himself and blesses. It follows that he is “not commanded but does.”