"If a man (adam) will have on his flesh...a tzara'as affliction...he shall be brought to Aaron the Kohen or to one of his sons the Kohanim" (Tazria 13:2.) Why does the Torah begin its discussion of the laws of tzara'as with the word adam? It should have used the more common word ish.
Chazal(Arachin 16a) identify seven different aveiros that can cause tzara'as, the most famous of which is lashon hara. Why does a person speak lashon hara if he knows that it is forbidden? Sometimes he simply loses control. Before he realizes, the words just tumble out of his mouth. Perhaps that is why the Torah begins its discussion of tzara'as with the term adam because adam is often used in contrast to beheimah (animal), as in "Adam u'beheimah toshiya, Hashem - Hashem, You save man and animal" (Tehillim 36:7.) When a person speaks lashon hara, he acts instinctively and impulsively like an animal. By not exercising control over himself, he loses his special quality of adam and lowers himself to the level of beheimah. The Torah uses the term adam to indicate that to be cured of tzara'as, a person must act like an adam once again, to make the right choices in his actions and his speech.
The importance of acting like an adam and making the right choices in life is the very first message Hashem gives to Klal Yisrael in Mitzrayim. "Hachodesh hazeh lachem rosh chodoshim, rishon hu lachem l'chadshei hashana - this month (of Nissan) is for you the first of all months, the first of all the months of the year" (Shemos 12:2.) The Seforno explains that Hashem was saying, "From now on the months will be yours, to do with them as you choose. This is the first of all the months of the year because in this month you begin your bechirah (free will) existence." Hashem was telling Klal Yisrael, "Now that you are no longer slaves, you are not beholden to anyone. You have the free will to choose your direction in life! Use your freedom properly, to elevate yourself, not to satisfy every whim and desire of your heart."
This is what Chazal meant when they said, "Ein lecha ben chorin ela mi she'oseik b'Torah, v'chol mi she'oseik b'Torah mis'aleh - a person is not truly free unless he engages in Torah study, and whoever engages in Torah study becomes elevated" (Avos 6:2.) One who pursues his Torah study with dedication, and whose life is shaped and guided by a Torah perspective, is a true ben chorin because he understands that the ultimate purpose of freedom is to elevate himself through the choices that he makes.
While non-Jews can certainly elevate themselves by fulfilling the seven mitzvos of the bnei Noach, only Klal Yisrael have the ability to achieve the highest level of freedom by engaging in talmud Torah and observing all 613 mitzvos. Perhaps this is why only Klal Yisrael are subject to the rules of tumas tzara'as (Negaim 3:1, 12:1). The Tosafos Yom Tov (ibid) and the Ohr Hachayim (Tazria 13:2) explain this halacha based on the statement of Reb Shimon that only Klal Yisrael are referred to as adam in the context of tumas ohel. "Atem kruyim adam - only you are called adam" (Bava Metzia 114b.) Since the Torah also uses the term adam regarding tumas tzara'as, that halacha as well must be limited to Klal Yisrael.
This does not mean that non-Jews are never called adam. The fact is the Mishna (Avos 3:14) declares "Chaviv adam she'nivra b'tzelem - man is beloved because he was created in the image of G-d." The Tosafos Yom Tov and the Tiferes Yisrael both explain that even non-Jews are called adam in this context because they also have mitzvos. But Klal Yisrael have an elevated status of adam because they have a larger group of mitzvos to fulfill, and consequently they have the potential to rise to an even higher spiritual level.
Yet that privilege does not come without responsibility. If a Jew chooses to develop his neshama, to perfect his middos, to dedicate his life to talmud Torah and spiritual pursuits, he can rise to the highest levels. But if he fails to live up to his spiritual potential, and he allows his physical side to dictate his actions and his speech, then he falls to an even lower level than a non-Jew, and he is subject to the laws of tumas tzara'as.
The yom tov of Pesach, zman cheiruseinu, is a time to rediscover the essence of true freedom. When we liberate our neshamos from their physical limitations, and we allow them to express themselves through mitzvos and ma'asim tovim, we infuse our lives with meaning and purpose, and we become truly worthy of being called adam in the fullest sense of the word.