Thought from Today's Old Testament Passage:
The Book of Leviticus has very little narrative, but is filled with instructions, rituals, regulations, and laws. This chapter  offers a change of pace in the reading for it is a narrative. However, the interest is almost obliterated because it is a horrible tragedy which is recorded here.
This is another blot on man's long and sordid history of sin and willfulness. It is the record of the rebellion and disobedience of the two sons of Aaron. It follows the glorious day of dedication recorded in the preceding chapter. So often we find this happening. After a flush of victory, there is defeat—as in the Book of Joshua, the victory of Jericho is followed by the ignoble defeat of Ai.
The presumption of Nadab and Abihu is frightening in the light of the clear teaching which God gave at Sinai. "And let the priests also, which come near to the Lord, sanctify themselves, lest the Lord break forth upon them" (Exod. 19:22). In Exodus 30:34-38 God gave to Moses the formula for the incense to be used in the tabernacle and said, "As for the perfume which thou shalt make, ye shall not make to yourselves according to the composition thereof: it shall be unto thee holy for the Lord. Whosoever shall make like unto that, to smell thereto, shall even be cut off from his people" (Exod. 30:37-38).
The holiness of God is set forth at the beginning of the age of law by this incident. The holiness of God is set forth at the beginning of the age of grace by the incident concerning Ananias and Sapphira. Death was the drastic penalty in both cases. Our God is holy, and He deals with His children on that level. "For our God is a consuming fire" (Heb. 12:29) is something we all need to learn today. "Knowing therefore the terror of the Lord, we persuade men …" (2 Cor. 5:11). This is something we need to recognize today.
J. Vernon McGee, Thru the Bible Commentary [computer file] electronic ed., Logos Library System (Nashville: Thomas Nelson) 1997, © 1981 by J. Vernon McGee