Joy as the source of Divine inspiration

ואיתא שמחת בית השואבה שמשם שואבין רוה"ק.

It is taught regarding the Simchas Beis HaSho'eivah (the Rejoicing of the Water-Drawing) that from there one draws ruach hakodesh (Divine inspiration).

The Sefas Emes notes the Chazal that the joy of the water-drawing celebration in the Bais Hamikdash was a wellspring from which people could draw ruach hakodesh.

משם היינו מתוך זו השמחה כמ"ש ברמב"ם.

"From there" means: from within this very simcha, as the Rambam writes.

The phrase "from there" is not merely about the place; it teaches that the simcha itself is the source from which ruach hakodesh is drawn, as the Rambam stresses.

מדכתיב תחת אשר לא עבדת בשמחה כו'.

This is derived from what is written: "Because you did not serve Hashem... with simcha..." (Devarim 28:47).

The Torah's rebuke for failing to serve "with joy" proves that simcha is not a side benefit but an essential component of avodah.

מוכח שיש שמחה המביאות לעבודת השי"ת ע"ש.

This proves that there is a simcha which brings one to the avodah of Hashem; see there.

Joy is a vehicle: the right kind of simcha actively leads a person into proper service of Hashem, which is why its absence is so grave.

ונרמז בפסוק ורוח אלקים מרחפת על פני המים היינו ניסוך המים דסוכות כנ"ל:

And this is hinted at in the verse "and the spirit of God hovered over the face of the waters" (Bereishis 1:2) — this alludes to the nisuch hamayim (water libation) of Sukkos, as explained above.

The "spirit of God" hovering over the "waters" at creation hints at the ruach hakodesh drawn through the water-libation joy of Sukkos — the simcha of the water itself summons the Divine spirit.

Summary: The Simchas Beis HaSho'eivah teaches that simcha is itself the wellspring of ruach hakodesh. As the Rambam stresses and the verse "you did not serve with joy" proves, true joy is an essential part of avodas Hashem — hinted at in "the spirit of God hovering over the waters," alluding to the water libation of Sukkos.