A person is not the body -- which we see -- but the soul -- which we cannot see. It is the soul that gives life to the body and activates it. And it is the soul that understands; knows; feels; and, in general, experiences. While the soul has no physical shape, it does have the same structure as the physical body, but in spiritual form: it, too, has 248 "limbs and organs"; and 365 spiritual "veins, arteries and sinews."
The physical body is a garment tailored to the form of the soul, much like physical items of clothing are made to fit the needs of the body. Thus the soul is cloaked in the body. It then energizes the body and guides it -- like an ax in the hand of a woodchopper -- in what ever it does or senses. This is why when the soul departs, the body becomes a paralyzed, lifeless corpse: "Thus the dust returns to the ground, as it was, and the spirit returns to God who gave it (Ecclesiastes 12:7).
Just as the body needs of food and air to live and flourish, so too, the soul needs "food and air" for nourishment. But since it is a spiritual entity, its food and air are also spiritual. What is its food? The positive mitzvot of the Torah. There are 248 positive mitzvot in the Torah, parallel to the soul's 248 limbs and organs. Indeed, each mitzvah has a counterpart limb or organ in the body that resembles the mitzvah in some way. Thus, there is a direct correlation between mitzvot and life -- "You shall keep My statutes and laws which a person shall do and thereby live [forever]" (Leviticus 18:5).
Everything in the universe was created by an utterance of the Creator, may He be blessed. In fact, everything that exists needs His constant flow of bounty for it to continue. This continued sustenance also comes from the "breath of the Creator’s mouth," as is written, "Forever, God, Your word stands firm in the heavens" (Psalms 119:89)...
But in order for man to receive this flow of sustenance, he must be connected to God. How does man connect to God? When he performs good deeds. Good deeds have the power to draw a holy, spiritual sustenance known as the "light of God," which shines upon the person and infuses his soul with life...
And just as the body has veins and arteries -- conduits for the blood that transports the nourishment needed by the organs -- so too, the soul has "veins and arteries." And just as the physical veins and arteries can become clogged or diseased if the person does not eat healthy and nourishing food, so too, the spiritual veins and arteries can become "clogged or diseased." Healthy food for the soul is the positive mitzvot, and the poisonous food is the prohibitions of the negative mitzvot. There are 365 negative commandments, corresponding to the 365 conduits of the soul.
This correspondence alludes to the fact that sins clog and block the arteries of the soul, preventing the spiritual "blood" from reaching the spiritual organs, and cutting them off from the vital nourishment they need in order to live. Some sins can also actively poison and kill various organs of the soul. Finally, when a person's sins are very numerous, they can even kill his entire soul -- just as a severe physical illness can kill an entire body.
It is natural for humans to seek pleasure. A person will not do anything unless he expects to get some benefit from doing the action. Yes, there are people who will live a life of privation, but only when they believe that a hardship is but a temporary price for ultimately achieving more lasting pleasure. People therefore crave expected pleasure -- and call it "good" -- and dread of the lack or loss of pleasure -- and call it "bad."
How pleasure is measured is a purely subjective matter, of course, for each individual will measure pleasure in accord with his own tendencies, senses and desires. And since people equate pleasure with goodness, what they judge as good or bad will also depend on their personal bent and on the intensity of what they consider pleasurable. This is why the concept of "good" varies between people, and depends on such factors as age, intellect and temperament, or on the emotions of jealousy, passion and glory seeking. For these are the roots of a person's desire, which in turn will guide his leisure and dictate on what he will spend his energy; the activities in which he will engage; and to what he will be sensitive.
Children, for example, are drawn to childish games; most often they are attracted more to games and other diversions than they are to activities that would be truly beneficial for their health (such as proper diet and appropriate relaxation), or for their future (such as going to school and learning in general). Adults, though, scorn of the desires of children, which they consider petty, yet they take their own desires for food and drink etc. very seriously. Then there are adults who consider themselves more sophisticated than the average adult, so they will scorn other adults. To them, the pursuit of money and fame is what is really important. And so on.
As long as a person is not accustomed to true spiritual life and to spiritual food, he will think that the only "good" in the world is physical pleasure. He will also think that the only aspects of reality that exist are physical and corporeal things. Furthermore, such a person views belief in the existence of spirituality a fantasy and calls spirituality a myth...