Avraham's unquenchable love kept holiness alive

במשנה בעשרה דורות עד שהביא המבול.

In the Mishnah: "There were ten generations from Adam to Noach… until He brought the Flood (mabul)" (Avos 5:2).

The Sefas Emes opens with the Mishnah counting the ten generations leading to the Flood and then to Avraham.

ובי' דורות עד שבא אברהם וקיבל שכר כולם דכתיב מים רבים לא יוכלו לכבות האהבה ולכן גברה אהבת אאע"ה שלא יכלו הרשעים לכבותה ונשאר הקדושה בעולם בכח.

And [there were another] ten generations until Avraham came and received the reward of them all, as it is written: "Many waters cannot extinguish the love" (Shir HaShirim 8:7) — therefore the love of Avraham Avinu prevailed, for the wicked could not extinguish it, and the kedushah remained in the world in potential.

Avraham received the reward that all those generations failed to earn. His love for Hashem was the "love that many waters cannot quench"; the wickedness of his era could not extinguish it, and through him holiness survived in the world, at least in latent form.

דהאדם כולל כל העולם בפרט הצדיק וכמו שבלבו הי' התלהבות יותר מן הטבע.

For the human being includes the whole world, especially the tzaddik; and just as in his heart there was an enthusiasm (hislahavus) beyond nature —

A person, and above all a tzaddik, is a microcosm containing the entire world. Avraham's heart burned with a supernatural ardor for Hashem.

כך נתגלה הנהגה זו בכל העולם ועל זה אמרו חסיד המתחסד עם קונו.

— so this conduct became revealed throughout the whole world; and concerning this they said: "a chassid is one who acts with chesed toward his Maker."

Because the tzaddik mirrors the whole world, the fiery love in Avraham's heart radiated outward into all creation; he is the "chassid" who pours kindness even toward his Creator.

ובאמת הי' התחלת ב' אלפים תורה דאיתא עבירה מכבה מצוה ואינה מכבה תורה וזה הי' הפרש בין נח לאברהם אע"ה:

And in truth this was the beginning of the "two thousand years of Torah," as it is taught: a sin (aveirah) extinguishes a mitzvah but does not extinguish Torah — and this was the difference between Noach and Avraham Avinu.

Avraham inaugurated the era of Torah. Since "many waters" (sin) can quench a mitzvah but never Torah, Avraham's Torah-rooted love was unquenchable — whereas Noach, on the level of mitzvos alone, did not leave enduring kedushah in the world as Avraham did.

Summary: Across the twenty generations from Adam, Avraham alone "received the reward of all," for his love of Hashem was the love that "many waters cannot extinguish." As a tzaddik who is a microcosm of the world, his supernatural ardor radiated into all creation and kept holiness alive. Avraham began the era of Torah, and the key difference between him and Noach is that sin can quench a mitzvah but never Torah — so Avraham's love endured where the generations of the Flood were washed away.