Purifying the heart to receive Torah

איתא בזוה"ק אמור דבליל שבועות משפיעין משמים טהרה ללבות בני ישראל המקוין לטהרה.

It is stated in the Zohar HaKadosh (Emor) that on the night of Shavuos a taharah (purity) is poured down from Heaven into the hearts of Bnei Yisrael who hope and yearn for taharah.

The Sefas Emes begins with the Zohar's teaching that Shavuos night brings a Heavenly gift of purity into the hearts of those who long for it — purity is granted to those who desire it.

דכמו שהי' בשעת מתן תורה מקודם פרישה כדכתיב לך כו' וקדשתם כו' כן בכל שנה.

For just as at the time of Mattan Torah there was first a separation, as it is written, "Go… and sanctify them…" (Shemos 19:10), so it is every year.

Before receiving the Torah at Sinai, Bnei Yisrael had to first prepare through prishus (separation) and sanctification. That same preparation is required anew each year before Shavuos.

וכן כל ימי הספירה לטהר הלב להיות כלי מוכן לתורה כמ"ש לב טהור ברא לי אלקים אח"כ ורוח נכון חדש זה התורה.

And so too all the days of Sefirah are to purify the heart, to become a fitting vessel for the Torah, as it is written, "A pure heart create for me, O God," and afterward, "and renew a steadfast spirit within me" (Tehillim 51:12) — this latter is the Torah.

The forty-nine days of Sefiras HaOmer are a process of cleansing the heart so it can serve as a vessel ready to receive Torah. First comes the "pure heart"; only then the "steadfast spirit," which the Sefas Emes identifies with the Torah itself.

ואיתא אש שחורה על גבי אש לבנה והוא טהרת הלב כמ"ש וכבסו שמלותם ויחורון לבושיהון כי הלב הוא כלי ולבוש לקבל הפנימיות וכפי טהרת הלב כן נרשם חקיקת התורה כמ"ש הלומד ילד כדיו כתוב על נייר חדש כו':

And it is stated that the Torah is "black fire upon white fire" — and this [white fire] is the taharah of the heart, as it is written, "and they shall wash their garments," which the Targum renders "and they shall whiten their garments" — for the heart is a vessel and a garment to receive the penimiyus (inner content), and according to the purity of the heart, so is the engraving of the Torah inscribed, as it is said, "One who learns as a child is like ink written upon fresh paper."

The Torah is "black fire on white fire" — the black letters of Torah need the clean white surface of a pure heart to be inscribed upon. Washing the garments symbolizes whitening and purifying the heart, which is the "garment" that receives the inner light. The cleaner the heart, the clearer and more lasting the impression of Torah — like fresh ink on new, unsmudged paper.

Summary: Shavuos night brings a Heavenly outpouring of taharah into the hearts of those who yearn for it. Just as Mattan Torah required prior preparation and sanctification, the days of Sefirah are meant to purify the heart into a fitting vessel for Torah. The Torah, "black fire on white fire," is inscribed upon the white surface of a pure heart — and the purer the heart, the clearer and more enduring the imprint of Torah, like ink on fresh paper.