In introducing the first mitzvah given to us as a people, the mitzvah of sanctifying the new moon, the Torah also introduces a new term -- Adas Yisrael (Shemos 12:3).
Rabbi Joseph B. Soloveichik zt"l ("The Rav" as his students call him) wrote a teshuvah titled "Orthodox, Conservative and Reform Jews in the United States: Second article in a series on Responsa of Orthodox Judaism in the United States". It is only available as a 7 page Xeroxed copy of type-written pages, not dated -- although the Rav refers to a proposal he presented at an RCA conference "this past summer" that a footnote associates with the summer of 1954 convention.
In true Brisker derech [the style of learning created by the Rav's grandfather, R. Chaim Brisker], the Rav divides the concept of the unity of the Jewish people into "tzvei dinim" [two laws]. The first he associates with the term "eidah" [congregation], which he relates to the words "eid" and "eidus" [witness, testimony]. The second is that of the "am" [nation], from "im" [with].
What unifies us as an eidah is "the unity of Jews as members of a spiritual community", of being a "kingdom of priests and a holy nation", as decreed at the end of the revelation of Sinai. "A collective testimony united us all into a Jewish community. It therefor goes without saying, that the Jew, who erases from his memory this great testimony, and destroys the unique collective tradition, breaks the tie which joins him with the Jewish community as a congregation [eidah], as a spiritual Jewish entity."
Rabbiner Samson Rephael Hirsch, in his commentary on our verse, reaches a similar definition of the word eidah but does so using a different etymology. He finds the root to be ya'ad, to fix or appoint. "A society united by their common calling."
I would like, if I may, to add to the Rav's thought by pointing out that the proof provided in the Gemara that a minyan requires 10 men is also based on the word "eidah", which is compared to the "eidah" used to describe the 10 spies who slandered the Land of Israel. A collection of 10 men, by becoming an eidah, are able to perform things that require the collective sanctity of Bnei Yisrael.
The second concept is that of "am" -- "Am livadad yishkon" we are a nation that dwells alone. Is is "in our historical transmigrations and in our paradoxical fate. Our history would not fit into a different historical framework, and out fate is incomprehensible." This entity predates Sinai, "And I shall take you unto me as a nation [am], and I shall be unto you a G-d" (Ex. 6:7).
The preceeding story of the exodus, which opened with the expression Am B'nei Yisrael (Shemos 1:9), was about the Jewish people as a historical unit. That is why we are referred to as an am. Now, with the first mitzvah given to the Jewish people, we fain the second element, that of being a religious unit, and are called Adas Yisrael, the eidah of Israel for the first time.© 1995 The AishDas Society