Our Gemara on Amud Aleph discusses the famous principle of קדש עצמך במותר לך , to achieve a state of holiness by a abstaining even from that which is permitted. Although not exclusively, much of the applications of this principle is used in regard to sexuality, as in our Gemara and Rashi in the beginning of Parashas Kedoshim. The simple and best understanding of this is that indulgence without any restraint, even in matters that are technically permitted, will lead to a mindset and attitude that is self absorbed and primed for actual sin. Lust usually leads to more lust and less satisfaction, which then leads to more boundary pushing to meet needs that can never be satisfied.

Though a positive commandment, the Torah did not itemize what should be prohibited because it depends on individual temperament and choice. How much to indulge, and how much to abstain?

One of the most famous Gemaras about sexual abstention is in Nedarim 20, where a long list of behaviors are proscribed, such as refraining from different sexual positions that are seen as animalistic and other lustful behaviors. The overall feel is that sexuality should be treated in a sacred manner. Somewhat confusingly, the Gemara offers a different opinion, that all that one wishes to do together with his own wife is permitted. Ramah understands this to mean, technically it’s permitted but it is appropriate to abstain, likely along the same lines as we saw above  קדש עצמך במותר לך (See Shulkhan Arukh EH:25:2). Rambam In his commentary on Mishna Sanhedrin (7:4) explains this in a similar manner.

The Shittah Mekubetzes (Op. Cit.) offers a perspective which is difficult to understand in light of what we have seen. He states the following as a comment on that statement of the Gemara

כל מה שאדם רוצה לעשות באשתו עושה. ואין חסרון קדושה. 

One may conduct himself as he wishes with his wife and it is not a diminishment of holiness.

This is a departure from the approach of the Rama and Rambam. Unlike the Rama and Rambam that all forms of sexual expression between husband and wife are technically permitted, but it is still holier to practice abstention. The Shittah states that to conduct oneself as he wishes is not even a diminishment of kedusha. How could this opinion be tenable?

The Yismach Moshe at the beginning of Kedoshim says that there are two ways to fulfill קדש עצמך במותר לך based on two ways of reading the phrase. The simple peshat is, “Make yourself holy by abstaining from that which is ordinarily permitted.” However, literally the phrase can be read as, “Make yourself holy THROUGH that which is permitted.” He explains, sometimes the best way to keep yourself holy and avoid sinking is by allowing yourself the permitted pleasures in order to satisfy desires. He says, such indulgences performed with the proper intent, that is to be reasonably gratified in order to not succumb to sin, is also a method to become holy.