Testifying that all creation belongs to Hashem

במדרש בני חת עשר פעמים על ידי שביררו מקחו של צדיק נגד עשרת הדברות.

In the Midrash: "the sons of Cheis" are mentioned ten times — because they clarified (confirmed) the purchase of the tzaddik — corresponding to the Aseres HaDibros (Ten Commandments).

The Midrash observes that "Bnei Cheis" appears ten times in the account of Avraham purchasing the Me'aras HaMachpeilah. Because they affirmed and ratified the tzaddik's acquisition, they earned a parallel to the Ten Commandments. The Sefas Emes will draw out the inner meaning of this "clarifying the tzaddik's purchase."

הוא רמז לבני ישראל שזוכין לברר מקחו של צדיק חי עולמים.

This is a hint to Bnei Yisrael, who merit to clarify the purchase of the Tzaddik, the Life of the worlds.

Beyond the literal sale, this alludes to the mission of Bnei Yisrael: to "confirm the purchase" of the ultimate Tzaddik — Hashem, "Chei Olamim," the Life of all worlds. The Jewish people testify to and ratify that the entire world belongs to its true Owner.

שבנ"י מעידין בכל יום כי להשי"ת העולם ומלואו.

For Bnei Yisrael testify each day that the world and all its fullness belong to Hashem.

Every day, through Krias Shema, tefillah, and brachos, Bnei Yisrael bear witness that the world and everything in it is Hashem's. This daily testimony is how they "clarify the purchase" — establishing publicly that Hashem is the true Owner of all.

והוא קונה הכל.

And He is the Acquirer of all.

Echoing "Koneh shamayim va'aretz" (Acquirer of heaven and earth), the point is that Hashem alone is the true Owner and Master of everything. The world is, as it were, His "purchase," which Bnei Yisrael are charged to affirm.

וצריכין ללמוד מזה שהפסוק מאריך השדה וכל העץ אשר בשדה שצריך האדם להעיד על כל דבר פרטי שיש בעולם להתקשר הכל בהשי"ת:

And we must learn from this — that the verse elaborates, "the field and every tree that is in the field" — that a person must bear witness on every single detail that exists in the world, to bind everything to Hashem.

The Torah's seemingly excessive detail — listing "the field and every tree in the field" in Avraham's purchase — teaches that our testimony must extend to every particular thing in creation. A Jew's avodah is to recognize Hashem in each individual detail of the world, binding even the smallest object back to its Source.

Summary: The tenfold mention of "Bnei Cheis" confirming Avraham's purchase, paralleling the Ten Commandments, hints that Bnei Yisrael are tasked to "confirm the purchase" of the ultimate Tzaddik — Hashem, Owner of all — by testifying daily that the world is His; and the Torah's detailed listing of "the field and every tree" teaches that this testimony must reach every single detail of creation, binding all of it back to Hashem.