178. Three Partners in Man
Concerning the three partners in man: the Creator, father, and mother.
And he said that there is a fourth partner: the earth. If one does not take nourishment from the earth, one cannot persist. Earth is considered Malchut, which is generally considered having four discernments, called HB TM. And the nourishment one takes off the earth is the scrutinies, whereby the nourishment, the food, is separated from the Klipa (shell).
There are two discernments in Malchut: 1) Kedusha (Sanctity); 2) The Evil Lilith. Hence, when a person eats and makes the first and last blessings, the food is thus brought out of the dominion of the Sitra Achra. And since the food becomes blood, and blood is considered Nefesh, his Nefesh is now secular, and not of the Sitra Achra.
However, when one eats of a Mitzva meal, when the food is considered Kedusha, if he eats it with intention, the food becomes blood, and the blood becomes Nefesh. And then he comes to a state of Nefesh de Kedusha. This is why the evil inclination always comes to a person and makes him understand that it is not worthwhile to eat at a Mitzva meal for several reasons. Its primary intention is to not eat at a Mitzva meal for the above reason, since it is a part of Kedusha.