Earlier, we discussed how the greatest pleasure of all is to be found in drawing close to holiness and G-dliness.
Aside from being inherently true, this is also an argument that one who feels mired in physical lusts can use to convince his Bestial Soul to devote itself to the spiritual.
However, there is a price to pay. In order to experience a higher pleasure, one must be more refined. Just as one who always drinks cheap, low-grade wine will not be able to sense the richness of flavor in fine wine, so must the one who wants to experience holy pleasures divest himself of physical pleasures. To use Kabbalistic terminology: In order for the vessel to absorb a higher light, it must be more refined.
Indulgence in physical pleasures, even technically permitted ones, cools off the fire and passion one should have for holiness, and spoils one’s refined taste for G–dliness. This is the reason that physical pleasures are referred to as “the river of Shitim.” A river represents water, for pleasures stem from water, which causes plants that provide pleasure to grow. The word Shittim is related to the Hebrew word shtus, foolishness, for physical pleasures are foolish. The reason for this is twofold: Many physical pleasures lead to a bitter end, and even those that don’t stem from a very low source.
We can elaborate on the latter point through delving into the Shabbos liturgy. There we recite, “May all my innards [praise] His [G–d’s] Holy Name.” “My innards” is a reference to the angels called kravayim, innards. These angels are compared to the intestines, which digest the food one ingests, refining the important nutrients from the unneeded ones, and then absorbing the former into the body and eliminating the latter through defecation. Likewise, the angels receive a divine revelation that contains certain elements that are of low quality that they cannot internalize; this is spiritual waste matter. Certain angels are appointed with the task of refining the nutrients from the waste, and eliminating the waste matter. This rejected spiritual energy then falls down into our world, and turns into physical pleasures.
This is the reason that physical pleasure is referred to as foolishness, for in reality it is the waste matter from the higher spiritual realms. The foolishness of the hedonist is even greater when he is aware that physical pleasure will detract from his ability to experience G–dly pleasure. This is tremendous foolishness, for this means exchanging physical pleasure, which is in reality on the level of waste matter, for divine pleasure, which is true pleasure.
Let us be wise and avoid indulgence in physical pleasures, enabling us to develop refined pleasures and thus bring true delight and fulfillment to our soul.
 The rest of this post is based on Sefer HaMa’amarim Basi L’Gani, Vol. 1, p. 50.