Torah actualizes and renews creation on Shavuos

וביום הביכורים.

"And on the day of the first-fruits (yom ha'bikkurim)."

The verse refers to Shavuos, called the day of the bikkurim, the festival of the giving of the Torah.

כי תכלית בריאת שמים וארץ הי' בעבור התורה כמ"ש בשביל התורה שנקראת ראשית ולכן ביום זה נגמר עיקר המכוון שהוציא הבריאה הפנימיות מכח אל הפועל.

For the purpose of the creation of heaven and earth was for the sake of the Torah, as it is said: "For the sake of the Torah, which is called reishis (the beginning)" — and therefore on this day the essential intent was completed, that the inner dimension (penimiyus) of creation was brought from potential into actuality.

Creation itself exists only for the sake of the Torah (Rashi on "Bereishis" — "for the sake of Torah called reishis"). On Shavuos that ultimate purpose was realized: the hidden inner core of creation was actualized through the giving of the Torah.

וממילא כשניתקן העיקר ניתוסף כח והתחדשות בכל.

And consequently, when the essential core was rectified, strength and renewal (hischadshus) were added to everything.

Once the essential purpose of creation was set in place through Torah, a new vitality and renewal flowed into all of creation.

כמ"ש מחדש בטובו בכל יום מעשה בראשית.

As it is said, "He renews in His goodness, each day, the work of creation (maaseh bereishis)."

This echoes the daily blessing that Hashem continually renews the act of creation every single day.

וכתוב בספרים בטובו זו התורה שבכח התורה הקב"ה מחדש בכל יום הבריאה.

And it is written in the sefarim that "in His goodness (b'tuvo)" refers to the Torah — for through the power of the Torah, Hashem renews the creation each day.

The holy works explain that "His goodness," through which creation is daily renewed, is the Torah itself; Torah is the very force that sustains and refreshes the world.

ומכש"כ ביום זה שניתנה בו תורה.

And all the more so on this day, on which the Torah was given.

If Torah renews creation every day, then surely on Shavuos — the very day of mattan Torah — this renewing power is at its peak.

ולכן צריך להיות מקודם טהרה ימי הספירה שהם לטהרה עפ"י מ"ש לב טהור ברא לי כו' אחר כך ורוח נכון חדש בקרבי:

And therefore there must be purification beforehand — the days of Sefiras Ha'Omer, which are for purification (taharah) — in accordance with what is said, "Create for me a pure heart… and renew within me a proper spirit."

To receive this renewing power of Torah, one must first be purified; that is the role of Sefiras Ha'Omer. The verse's order mirrors this: first "create a pure heart" (the cleansing of Sefirah), and only then "renew within me a proper spirit" (the renewal of Shavuos).

Summary: Shavuos, the day of bikkurim and mattan Torah, is when the very purpose of creation — to bring forth its inner penimiyus through Torah — was actualized. Since Torah is "His goodness" through which Hashem renews creation daily, that renewing power peaks on Shavuos. But it requires prior purification: the days of Sefiras Ha'Omer cleanse the heart ("create for me a pure heart") so one is ready for the renewal of "a proper spirit" at Sinai.