Vayikra 16:1
The LORD spoke to Moses after the death of the two sons of Aaron who died when they drew too close to the presence of the LORD.
Rabbi Adin Steinsaltz
The cause of the sin was overfamiliarity with God and His service. … [The Priests] run the risk of becoming habituated and overly familiar insiders. … The problem of jadedness due to habituation is universal. …The Kotzker Rebbe reportedly explained the words of the piyut, “Beauty and eternity pertain to the One who lives forever,” that when a person looks at something beautiful a hundred times, it stops being special in his eyes. Beauty that lasts eternally pertains only to the One who lives forever.
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Someone once complained to me that despite his great interest in mysticism over the years, he always remained “on the outside” and never actually underwent any kind of mystical experience. He added, “The only thing that I have from all that I did is that every time that I say ‘Shema Yisrael,’ I feel a quiver.”
Now, this person is no rabbi, and is certainly not considered pious. Yet how many truly pious Jews can say that every time they recite “Shema Yisrael” they feel a quiver? The reason this happens is that we are too near, too habituated; even the holiness of the recitation of the Shema has become banal and mundane.
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Every person, in one respect or another, draws close to God, and one must always remember that even though he may know what goes on behind the scenes, he must not lose the feeling of respect and awesome reverence; he must not feel that he is exempt from the duty of keeping his distance. … Is one capable of being on both sides simultaneously — to be inside, and nevertheless to feel like an outsider who has entered for the first time, knowing nothing of the experience?
There is a perpetual partition between the sacred and profane, between the awesome and the ordinary. For the Priest, this partition is not smaller, but it is more difficult for him to abide by.
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Rabbi Nachman of Breslov comments that in order to achieve this, one must be simultaneously extremely old and yet, in a sense, completely infantile.
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The Talmud says of Aaron’s sons: “Only their souls were burned, but their bodies remained intact” (Sanhedrin 52a). This kind of death can befall any of us today as well — one continues to fulfill mitzvot, to sway during prayer, but his soul has burned up and left him.
Vayikra 18:3-5
You shall not copy the practices of land of Egypt where you dwelt, or of the land of Canaan to which I am taking you; nor shall you follow their laws. My rules alone shall you observe, and faithfully follow My laws: I the LORD am your God. You shall keep My laws and My rules, by the pursuit of which man shall live: I am the LORD.
[The Torah then proceeds to list various prohibitions concerning sexual behavior.]
Rabbi Yehudah Leib
The passage is difficult: If it refers to the forbidden sexual liaisons that are about to be explicitly listed, why does it make them dependent upon “the deeds of Egypt and Canaan”? Rather, the intent is that in all of our deeds we not do things as they are done in Egypt and Canaan. Every deed has an inner and an outer side; the inner root of all things is surely holiness, since all was created for God’s glory. This innermost point has been given to Israel.
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“the things a person shall do and live by them”: for by doing them you fulfill your true image as a person.