And Nadab and Abihu, the sons of Aaron, took either of them his censer, and put fire therein, and put incense thereon, and offered strange fire before the Lord, which he commanded them not. And there went out fire from the Lord, and devoured them, and they died before the Lord. —Leviticus 10:1-2
Nadab and Abihu were not chosen to be priests because of their personal integrity or worth but because God had established the priesthood in Aaron's family. Their authority was dependent upon Aaron—a right of birth.
Acting independently they attempted to offer sacrifices without their father's presence or authority, assuming their sacrifices would be acceptable to God. God recognized their offering as "strange fire," offered from the mind and imagination of man, not ordained or recognized by Him. Nadab and Abihu had overstepped their role and rebelled against the authority God had established. The result was death.
Any work undertaken in rebellion will not flourish. If your service seems to be fruitless, ask God if you are truly following His will for your life or if you are offering Him strange fire.
Father, I do not wish to do anything of my own.
Remove all strange fire from my life.
Purify me with Your fire. Amen.