Sforno on Exodus 19:6/ספורנו על שמות י״ט:ו׳

1ואתם תהיו לי ממלכת כהנים, this will make you special for only you will be a kingdom of priests, by teaching and instructing all of mankind to call out in the name of G’d and for all to serve him together. This was to be a forerunner of what will happen in the distant future as predicted by the prophet Isaiah 61,6 “and you will be proclaimed ‘priests’ of the Lord.” This is also the true meaning of כי מציון תצא תורה, “the Torah emanates from Zion.” (Isaiah 2,3) [This statement is attributed to the nations of the world at that time.

2וגוי קדוש, never to disappear from the stage of history. You will continue forever to exist as one man, as it will be in the distant future of which the prophet Isaiah 4,3 said “those who survive in Zion and those who will be left over in Jerusalem, all those who are inscribed for life in Jerusalem- shall be called ‘holy’.” [the author is making the point that somebody called קדוש is by definition immortal. Ed.] Our sages in Sanhedrin 92 describe this concept in the following words: “just as He, the Holy One, is forever, so the Jewish people are forever.” It had been G’d’s intention to make the Jewish people immortal at the time of the revelation at Mount Sinai, giving them the status that Adam had enjoyed before he sinned. Alas, just as Adam had sinned and had become mortal in Gan Eden, the Jewish people sinned with the golden calf and suffered the same fate as first man. The disaster is documented in Exodus 33,6 “the Children of Israel had to divest themselves of their jewelry which had been given them at Mount Chorev.”