Joy as the vessel for drawing divine light

שמחת בית השואבה שמשם שואבין רוח הקודש כי השמחה הוא כלי לשאוב מים חיים והוא רוח הקודש דכתיב ויפח באפיו נשמת כו'.

The Simchas Beis HaSho'eivah (Rejoicing of the Place of Drawing), from which one draws ruach hakodesh (divine inspiration) — for simchah (joy) is the vessel with which to draw living waters, which is ruach hakodesh, as it is written: "And He breathed into his nostrils the breath of life, etc."

The Sefas Emes explains that the festival's "drawing of water" was really a drawing of ruach hakodesh. Joy is the keili (vessel) that makes a person able to receive that flow of "living waters" — the inner soul-life that Hashem breathed into man at creation.

וכפי שאדם מתדבק בעיקר החיות שיש לו מהשי"ת מתפשט החיים בכל איבריו.

And to the degree that a person clings to the essential life-force he has from Hashem, that life spreads into all his limbs.

Every person has a core chiyus (vitality) flowing from Hashem. When one cleaves to that inner source through dveikus (attachment), the holy life-force radiates outward and animates the whole person, body and deed alike.

ואיתא לא ראינו שינה כדאיתא במד' על משה רע"ה שכל מ' יום שהיה בשמים לא הי' יכול לישון שידע שאין שיעור מה שיכול לקבל בכל שעה ושעה.

And it is taught, "we did not see sleep," as the Midrash relates concerning Moshe Rabbeinu, that during all forty days he was in heaven he was unable to sleep, for he knew there was no limit to what he could receive in every single hour.

The Simchas Beis HaSho'eivah was marked by sleeplessness, like Moshe on Har Sinai. When a person grasps that every moment holds boundless spiritual gain, he cannot bear to "sleep" through it — the awareness of constant opportunity keeps him fully awake and receiving.

וכן כתיב שבעת ימים בשנה על ימי הסוכות מה שלא נאמר כן בכל הרגלים.

And so too it is written "seven days in the year" regarding the days of Sukkos — something not said of any of the other festivals.

The Torah singles out Sukkos with the phrase "seven days in the year," a designation given to no other Yom Tov. This hints that these particular seven days hold a unique role within the entire year.

שעיקר הארת השנה תלוי' בז' ימים אלו.

For the essential illumination of the whole year depends on these seven days.

These seven days of Sukkos are the source from which the spiritual light of the entire coming year is drawn. What a person attains here radiates forward through all twelve months.

והכלי לקבל הוא השמחה:

And the vessel with which to receive it is simchah (joy).

The way to absorb this year-long illumination is through joy. Simchah is the open vessel that draws down and holds the abundant light made available during Sukkos.

Summary: At the Simchas Beis HaSho'eivah, joy serves as the vessel for drawing ruach hakodesh and the living life-force of Hashem; the unique seven days of Sukkos contain the illumination for the entire year, and it is specifically through simchah that a person becomes able to receive that boundless light.