The concept of the Jewish people being Hashem’s am segulah is first introduced in Sefer Shemot 19:5: “And now, if you obey Me and keep My covenant, you shall be to Me a treasure out of all peoples (segulah mikol ha’amim), for Mine is the entire earth,” and is echoed, as well, by David Hamelech in Sefer Tehillim: “For G-d chose Jacob for Himself, Israel for His treasure (l’segulato).
Little wonder, then, that Rashi explains segulah as “a beloved treasure, like ‘and the treasures of the kings’ (Sefer Kohelet 2:8), [i.e., like] costly vessels and precious stones, which kings store away. So will you be [more of] a treasure to Me than the other nations [Mechilta].” In contrast, Onkelos explains “segulah mikol ha’amim” as “and you shall be more beloved before Me than all the other nations (“u’tehon kadamai chabivin mikol am’maiyah”).
In sum, two classic approaches emerge concerning the meaning of the term segulah. For David Hamelech and Rashi, it connotes “treasure,” and for Onkelos it denotes the uniquely beloved status we have in the eyes of our Creator.
My rebbe and mentor, the Rav — Rabbi Joseph B. Soloveitchik zatzal (1903-1993) — in at least one instance, defines segulah differently than either Onkelos or Rashi, namely, as “singularity.
“The word ‘singular’ means ‘being only one,’ ‘exceptional,’ ‘extraordinary’ and ‘separate.’ The word segulah in Hebrew similarly connotes singularity. In Exodus (19:5), the Torah enunciates the doctrine of the election of Israel as a cardinal tenet of our faith.” (Rabbi Abraham R. Besdin, “Reflections of the Rav: Lessons in Jewish Thought Adapted from the Lectures of Rabbi Joseph B. Soloveitchik,” page 119)
As reflected by Rabbi Besdin, the Rav continues this line of reasoning, and emphasizes that segulah is not solely a theological construct. Moreover, it plays a crucial role in human interaction: