Bnei Yisrael Witnessing Creation

בפסוק ואעידה בם כו' פי' מו"ז ז"ל שע"י בנ"י מבורר שהקב"ה ברא שמים וארץ כדכ' אתם עדי כו' ונראה דב' הפי' אמת כדאיתא כשבנ"י זכאין הם מעידים בעצמם כו'

On the verse "And I will call as witness against them" (Devarim 31:28), my grandfather and teacher, of blessed memory, explained that it is through Bnei Yisrael that it becomes clarified and made evident that the Holy One, Blessed is He, created heaven and earth, as it is written, "You are My witnesses" (Yeshayahu 43:10). And it appears that both explanations are true, as it is taught that when Bnei Yisrael are meritorious, they themselves bear witness.

The Sfas Emes brings his grandfather's teaching that Bnei Yisrael are the living witnesses that Hashem created the world; he then adds that both ideas hold true together, since when Bnei Yisrael are worthy they testify by their very being.

ולכן בשבת קודש שנק' סהדותא ע"י שמתעלין בנ"י בש"ק למעלה מהטבע אז הם עדים על שמים וארץ

Therefore on the holy Shabbos, which is called "a testimony," through the fact that Bnei Yisrael are elevated on the holy Shabbos above the natural order, at that time they are witnesses upon heaven and earth.

On Shabbos, called a day of testimony, Bnei Yisrael rise above nature, and from that elevated place they are able to testify about heaven and earth themselves.

ובימי המעשה עוד בנ"י מקבלים הארה ע"י שמים וארץ כנ"ל

And during the weekdays of activity, Bnei Yisrael still receive an illumination by means of heaven and earth, as explained above.

On weekdays, by contrast, Bnei Yisrael draw their illumination through the medium of heaven and earth rather than standing above them.

אבל בשבת כ' ביני ובין ב"י אות ה"ל כי ששת ימים כנ"ל:

But regarding Shabbos it is written, "Between Me and Bnei Yisrael it is a sign forever, for in six days [Hashem made the heavens and the earth]" (Shemos 31:17), as explained above.

The verse marks Shabbos as the eternal sign between Hashem and Bnei Yisrael precisely because it recalls the six days of creation, which Bnei Yisrael testify upon.

Summary: The Sfas Emes builds on his grandfather's teaching that Bnei Yisrael serve as Hashem's witnesses that He created heaven and earth, as in "You are My witnesses." He reconciles two readings: Bnei Yisrael testify, yet they testify through their own elevated state when they are meritorious. On the holy Shabbos, which is itself called a testimony, Bnei Yisrael are lifted above the natural order and thereby stand as witnesses upon heaven and earth. During the weekdays, however, they receive their illumination only by means of heaven and earth. This is why Shabbos is the eternal sign between Hashem and Bnei Yisrael, for it recalls the six days of creation to which they bear witness.