"Kedoshim tihyu ki Kadosh Ani HASHEM Elokeichem" (19:2)
The medrash in Vayikra Rabbah expounds that once the pasuk said "kedoshim tihyu" you might have thought that you could reach the level of Hashem, kivyachol. So "ki Kadosh Ani" comes to teach us that the kedushah of Hashem is greater than than our kedushah- "Kedushati l'maala m'kedushatchem."
Here we see that were it not for this 2nd part of the pasuk, Bnei Yisrael would have thought we could attain the highest level of kedushah. We need a pasuk to tell us that only HB"H is on that highest level of kedushah.
Chazal teach in the medrash (B"R); R' Hosheiya said that when Hashem created Adam HaRishon, the Malachai HaSharet erred and wanted to say "kadosh" before him. Seemingly, before Adam sinned, he was on the highest level of kedushah to the point where the Malachai HaSharet wanted to say "kadosh" before him. They couldn't discern between HB"H and Adam HaRishon, kivyachol.
Pertaining to this, the Alter of Slabodka, R' Nosson Tzi Finkel zt"l, taught a fundamental concept: That even after Adam sinned with the Etz HaDaat and fell from his high madrega, the ability was always within him to rise back to his greatness. Similarly, we find that by Kabalat HaTorah, Bnei Yisrael returned back to they great and holy level of Adam HaRishon before his chet.
Ramchal writes in Mesilat Yesharim, someone who is kadosh - "nechshav k'mishkan k'mikdash u'k'mizbeach." - he is considered like a mishkan, mikdash, and a mizbeach. The food & drink of such a person are elevated to the extent that it is if they were really brought on the mizbeach.
The level that a person can reach is so great. Rambam writes (Hilchot T'shuva 5:2) that every person has the ability to be a tzaddik like Moshe Rabbeinu (Meaning: we can each reach our own personal highest level just as Moshe did). We have within our essence the power and ability to attain the loftiest heights of kedushah!
Every person has to realize the essence of his greatness, that we are created B'Tzelem Elokim, as well as his power and ability, to be a tzaddik like Moshe Rabbeinu. This realization will arouse within a person to not let his life and abilities to go to simply become hevel va’reik. Chazal teach (Tanna d’Bei Eliyahu) that every person has ask himself, “when will my deeds reach the level of the deeds of the avot; Avraham, Yitzchak, and Yaakov?”
Rabbeinu Yonah writes in sefer Shaarei HaAvodah, the first thing that a person needs to realize is his own level, and to recognize of the greatness of his ancestors; their gadlus and importance, as well as their closeness to Hashem. And once someone realizes this, he needs to constantly attempt to strengthen himself and to raise himself to this level. One needs to act in a way in which he will not bring shame to his ancestors and their ways and actions! When someone has a desire rise within him the chutzpah to do something that is not proper, he should ashamed for bring shame upon himself and upon his avot! He should tell his nefesh: “How can some as great and important as me, who has many good qualities, ben gedolim u’ben malchei kedem!- a son of great men and of kings of old, do such an evil thing. How can I sin to Hashem and to my avot?!” As explained by Rabbeinu Yonah, knowing one’s own level is the 1st fundamental thing a person needs to realize in order to distance himself from aveirot and to strengthen himself towards mitzvot. This concept is more influential than any other divrei mussar. Even more than contemplation (hisbonenut) for Yirat Hashem, omek hadin, or hefsed mitzvah k’neged scharah u’schar aveirah k’neged hefsedah!
