The Medrash (Rabbah 24:9) states: “’You shall be holy.’ You might think like Me; therefore, the pasuk states: ‘Because I am holy.’ My holiness is higher than yours.”
Rav Shlomo of Loitzk zy”a (Sefer Divrei Shlomo) explains that when Hashem commanded Klal Yisroel to be holy, they may have thought that they had to try to be literally like Him. Doing so would include going into impure place, as Hashem says about Himself (Vayikroh 16:16): “I am Hashem, who dwells with you within your impurities.” This is because Hashem is found in all place in the world, even in the most degraded and impure. Therefore, people might think that they must do the same.
To dispel this idea, the pasuk says: “Because I am holy.” Hashem tells us that His holiness is higher than ours, meaning that we could never be completely like Him. This is as is stated (Shemos 12:2): “And I passed through the land of Egypt – I and not a malach.” The Arizal (Likutei Torah, Tehillim 88) explains that even a malach would have been negatively affected by going through the depraved land of Mitzrayim. Therefore, Hashem went on his own. So too, no human being can dwell amidst impurity without being affected. Only Hashem can retain His kedusha no matter where He is. Accordingly, we are commanded to be holy on our level, wherever we are, but not to try to be as holy as Hashem.
