The two sons of Aharon who died were called Nadav and Avihu. The name Nadav (נדב) can be understood as “four sons” (ד-בן) - just as when the Pesach Aggadah says, “The Torah spoke of four sons,” it means these four sons, and they are Adam, Cain, Abel, and Seth. A further hint to this is in the name of Avihu (אביהוא), which means father (אבי) he is (הוא) - that is, Adam.
Thus, the two sons of Aharon were born to rectify whatever Adam and his three sons did not do correctly in their lifetimes, as their names hint to the following: Nadav means four sons, and Avihu means the father. They came to rectify Adam's faults, but instead, they were steadfast in them.
The first one was the fire. Before Adam married Eve, he was together with another woman, called Lilith. This is hinted at in Adam's words about Eve, "This one will be called a woman, because of her connection to the man." This one, but not the previous one. However, Lilith was not his true soul-mate, and this represented the wrong fire. As is known, a man (איש) and a woman (אשה) have a common element of fire (אש) between them. The additional letters - yud (י) in case of a man, and hei (ה) in case of a woman - constitute the name of God Yah (יה). If there is the presence of God (יה) in their union, and it is a true union, then this fire warms them, but if not, it burns them. Nadav and Avihu, too, brought an unauthorized offering of fire.
The second problem was wine. When Eve went to the tree of knowledge of good and evil – which was a grapevine – she squeezed out the juice of grapes and gave it to Adam in this form so that he would not know that it came from the forbidden tree. He should have understood this and stop himself, but he did not.
Nadav and Avihu, too, were drunk on wine when they brought their offering. This is hinted to in the very first phrase in this Torah portion, “Two sons of Aaron” (שני בני אהרן). If you take the last letters of the words, you get wine (יין). The first letters of the words "after... two sons" constitute “from fire” (מאש).
Later, Moses told Aharon that his sons were great, higher than Moses and Aharon themselves. He meant that they came from a higher source – Adam, while Moses came from Adam's son, Abel. They, therefore, had greater potential.
Art: Dutch School - A young boy holding a giant roemer of wine