What are the spiritual(mental), mystical, practical, realistic, religious social benefits of refraining from all perversions and immodesties?

Question

I should refrain from impure thoughts, licentious ruminations, immodesty and improper sex. I must guard my eyes, tongue and mouth from perversion and sexually improper 'things'. I must no watch porn, watch improper sexual acts, look at with lust other people, not read improper text, not listen to improper music and be Frum in my sexual conduct. Why?

What benefits does that give me or have when compared to the joy of following your Yetzer Hara (EI)? Why does it feel so good and what are the possible punishments for transgressions?

Answer 1

One of the places where the Torah warns us to not stray after our own hearts, can be found in Bamidbar 15:40. The Torah states

and that you seek not after your own heart and your own eyes, after which you go astray

Going after our heart, and lust after our thoughts, results in:

diverting of your rational souls from the paths of life eternal to the paths of destruction and death (Sforno, ad loc.)

If we are not going after our lusts, the reward for that is, as the Sforno explains:

והייתם קדושים לאלוקיכם, as a corollary you will be holy unto your G’d, deserving eternal life as He had meant for you to qualify for when He had said in Exodus 19,6 that “you should become for Him a nation of priests and a holy people.”

If we do this all, as you stated, the reward will be that we are holy unto G-d and deserving eternal life. This was all G-ds plan. So why not?

The Reishis Chochmah explains that if one cleaves and be led by the evil inclination, this is a "jump into the abyss" so to speak. It is very hard to get out of it. G-d does not want that, and thus He set boundaries for us to prevent us from sinning and keep falling/failing. To prevent that all the impulse of the thoughts of his heart was only evil continually.

The Rambam in his Guide for the Perplexed (Moreh Nevuchim 3:8) elaborates on the Talmudic teaching that:

Thoughts of transgression are worse than transgression (Yoma 29a)

The Rambam uses this principle and explains that:

When a person is disobedient, this is due to certain accidents connected with the corporeal element in his constitution; for man sins only by his animal nature, whereas thinking is a faculty of man connected with his form,—a person who thinks sinfully sins therefore by means of the nobler portion of his self: and he who wrongly causes a foolish slave to work does not sin as much as he who wrongly causes a noble and free man to do the work of a slave. For this specifically human element, with all its properties and powers, should only be employed in suitable work, in attempts to join higher beings, and not in attempts to go down and reach the lower creatures.

So, what he is meaning is that we have two sides: animalistic and holy. G-d does not want us to dwell on our animalistic side, rather, to dwell on the holy side. Why? Because we are made "b'tzelem elokim"- in the image of G-d. Do we want to use that image and behave immoral? Ofcourse not. So this is why we are not meant to stray in our thoughts.

Answer 2

Practical benefit is found Sanhedrin 107A;

ונתעלמה ממנו הלכה אבר קטן יש באדם משביעו רעב ומרעיבו שבע

But a halakha, i.e., a Torah statement, escaped him: There is a small limb in man that he employs in sexual intercourse. If he starves the limb, and does not overindulge, it is satiated; but if he satiates the limb and overindulges in sexual intercourse, it is starving, and desires more.

By following your desires you will never feel satisfied and always want more, by restraining them you will find yourself more satisfied and content.

Answer 3

First things first: We have not got any form of ownership over our sexual capabilities whatsoever without Hashem granting it. Every last detail of it, from physical to spiritual and beyond, is all something He made, He sustains, He provides, and He controls for us; sharing them from Himself, because only He can and we absolutely can't. So by answering this question about what's "in it for me to do this", I am not meaning to invalidate this point that it's not about us in the first place :)

Rav Melamed states the following in Peninei Halachah, Simchat Habayit U'Virchato 4:3:2:

שני צדדים ישנם בעוון הוצאת זרע לבטלה. מהצד הגלוי, הוא פחות חמור מחטאי ניאוף ושאר החטאים שקצבה עליהם התורה עונשים, מפני שבפועל הנזק שנגרם ממנו פחות חמור. אולם מהצד הפנימי, חטא זה מבטא את שורש כל הרעות, את שיא התאווה האנוכית שפוגעת באופן העמוק ביותר באמונה בה' ובאהבת הבריות. שכבר למדנו (א, ה-ו), שהפירוד הוא יסוד הקלקול שבעולם. הוא מתחיל בריחוק שבין הבורא לנבראים ונמשך לפירוד שבין הברואים. ולכן מצוות "וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ" היא "כלל גדול בתורה" (ויקרא יט, יח, ספרא שם), שעל ידה מתקנים את העולם כולו. ורק בין בני הזוג מצוות האהבה והאחדות מתקיימת בשלימות, ותמציתה בחיבור שבמצוות עונה (לעיל א, א). וזה עניינו של יצר החיים הזה שבין איש לאשה, שעל ידו בני הזוג פורצים את חומת האנוכיות, ומתקשרים זה אל זה באהבת אמת, והשכינה שורה ביניהם, וחיים וברכה נמשכים על ידם ממקור החיים ועד סוף כל הדורות (לעיל א, ד).

There are two dimensions of the sin of masturbation. On the surface, it is less severe than adultery and the other sins for which the Torah prescribes punishment, because, in practice, the damage caused thereby is not as grave. However, from the interior perspective, this sin reflects the root of all evil, the ultimate self-centeredness, which most profoundly impairs a person’s faith in God and his love for other people. As we have seen, detachment is at the root of all ruin in this world (1:5-6). It begins with the distancing between the Creator and His creations, and continues with detachment among His creatures. This is why the mitzva to “love your fellow as yourself” (Vayikra 19:18) is a “major principle of the Torah” (Sifra ad loc.), for it repairs the whole world. It is only in the spousal relationship that love and unity reach their complete fulfillment, and its essence is when they unite in the mitzva of ona (above, 1:1). This is the meaning of the life-giving impulse that exists between husband and wife, through which the couple breaks the walls of egotism and connects with one another with true love. The Shekhina dwells with them, and through them, life and blessing extend forth from Source of life to all future generations.

I haven't highlighted anything in specific because I think the entirety of this should be read. Aside from the previous sections that detail how it is likened to murdering one's children, it prevents one from greeting the Divine presence and having eternal life, and is impossible to repent for* (Zohar I 219b, 62a, SA EH 23:1), the root of all of the above comes from the darkening of one's soul and body that comes from this particular sin.

What it does most powerfully is it makes one self centered**, which blocks one from being able to relate to God, and Godly goodness, i.e. connection with true love. The true goodness and pleasure of Ona, which is what this aspect of our body and soul is designed for, cannot be accessed. It's a bitter irony, when a person seeks sexual pleasure, they are able to steal a tiny remnant of a memory of it, but the price they pay is they never actually get to experience it properly as the enjoyment of the mitzva of Ona is lost to them. They lose the very thing they want.

It dulls the soul and the body and life becomes uninteresting, tasteless, numb, all the vitality of their body that they remember from before they did this sin is nothing but an occasional nostalgic memory. The disconnection is the beginning of the end, as cynicism and apathy to life is death, and the beginning of everything on "that side", ch'v.

Ta'anug, pleasure, actually is the highest of the high of spirituality and even Godliness. It's the inner aspect of the crown of the sefirot, and it's expression in intimate relationships is the pinnacle of its holy purpose, so to speak, and this is similar to what Rambam stated in the source brought by Shmuel in his answer. Misusing it is therefore the foulest of all crimes, as I've heard many times in chassidic discourses.

So, even though there doesn't need to be, in Hashem's eternal kindness there are plenty of good reasons to not steal any sexual pleasure from the life Hashem gave us (and let's not forget that this affects our soul mate as well)! We have to trust His Torah and His intended way of using the gifts in life He gives us, and the advice of our sages, and our grandparents and put in the effort to build a holy intimacy in the way Hashem commanded us and we will see the truth of His words of what's so great about goodness and holiness, Oneness and intimacy.

^{* See this comment.
** not because masturbation is "loving oneself" (it's not, it's more like "imaginary relations"), but more to do with the fact that one is seeking one's own pleasure. Heard this point in a shiur from Rav Manis Friedman.}