Shabbos untouched by sin

ושמרו בני ישראל כו' הוא הבטחה ג"כ שבני ישראל ישמרו השבת.

"And Bnei Yisrael shall guard [the Shabbos]..." (Shemos 31:16) - this is also a promise (havtachah) that Bnei Yisrael will keep the Shabbos.

The Sefas Emes reads "v'shamru" not only as a command but as an assurance: Hashem promises that Bnei Yisrael will, in fact, keep the Shabbos - an eternal bond that cannot be wholly broken.

ואיתא כי מרע"ה מחזיר לישראל בש"ק הכתרים של נעשה ונשמע.

And it is brought that Moshe Rabbeinu returns to Yisrael on Shabbos Kodesh the crowns of "na'aseh v'nishma."

Chazal teach that the crowns Bnei Yisrael received for declaring "na'aseh v'nishma" at Sinai were taken away after the Cheit HaEigel; on each Shabbos, Moshe Rabbeinu restores these crowns to Yisrael.

נראה שבשבת לא קלקלו ע"י החטא.

It appears that on Shabbos they did not become damaged through the sin.

The fact that the crowns return specifically on Shabbos indicates that the dimension of Shabbos was never spoiled by the Cheit HaEigel - the sin did not reach that level.

ולכך שבת מעין עוה"ב כמ"ש בלוחות ראשונות חירות כו'.

Therefore Shabbos is a foretaste of the World to Come, as it says regarding the first Luchos, "freedom" (cheirus).

Because Shabbos remains untouched by sin, it is "me'ein Olam Haba" - a taste of the World to Come. This parallels the first Luchos, of which Chazal expound "charus" (engraved) as "cheirus" (freedom) - freedom from the yetzer hara and from death, a state the sin had not yet corrupted.

וכן איתא בחטא אדם הראשון שנתקבל בשבת.

And so it is brought regarding the sin of Adam HaRishon, that he was received [back in repentance] on Shabbos.

Similarly, Chazal teach that after his sin, Adam HaRishon's teshuvah was accepted on Shabbos - Shabbos itself interceded and brought him atonement.

ג"כ כנ"ל שלא הגיע החטא לבחי' שבת.

This too is as above - that the sin did not reach the aspect of Shabbos.

Here too the same principle applies: even Adam's sin did not penetrate to the level of Shabbos, which therefore retained the power to bring him back.

והוא ששבת במקום הגניזה כמ"ש מתנה טובה יש לי בבית גנזי כו' וכיון שנגנז לא הגיע קלקול החטא לשבת כנ"ל:

And this is because Shabbos is in the place of concealment (genizah), as it says, "I have a good gift in My treasure-house [and Shabbos is its name]" (Shabbos 10b); and since it is hidden away (nignaz), the damage of the sin did not reach the Shabbos, as above.

Shabbos resides in a hidden, treasured place - Hashem's "beis genazav" (treasure-house), as in the famous statement that Shabbos is the precious gift stored there. Precisely because Shabbos is "nignaz" (concealed and stored away above), it is beyond the reach of sin, and so it can restore the crowns and accept teshuvah.

Summary: "V'shamru Bnei Yisrael" is also a promise that Yisrael will always keep Shabbos. Because Shabbos resides in a hidden, treasured place - Hashem's "treasure-house" - the damage of sin never reaches it: not the Cheit HaEigel (so Moshe restores the crowns of na'aseh v'nishma on Shabbos), nor even the sin of Adam HaRishon (whose teshuvah was accepted on Shabbos). This is why Shabbos is a foretaste of Olam Haba and of the "freedom" of the first Luchos - an untouched dimension of holiness from which renewal and atonement flow.