"And Nadab and Abihu died before the LORD, when they offered strange fire before the LORD, in the wilderness of Sinai, and they had no children: and Eleazar and Ithamar ministered in the priest's office in the sight of Aaron their father." (Numbers 3: 4)
"Nadab" means "willingly" or "to incite, impel", and "Abihu" means "He is a Father". They died for offering strange fire to the LORD.
In the same way, we must stop trying to serve God in our strength, and see Him merely as "Father".
The second set of priests will explain how we should approach, or how we should see God.
"Eleazar" means "God has helped", and "Ithamar" means "Coastland of palms".
When we see God as our helper, as the One who works in and through and for us, then He can receive our service.
We see God as our helper when we see Jesus Christ and grow in grace and knowledge of Himself:
"25Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken: 26Ought not Christ to have suffered these things, and to enter into his glory? 27And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself." (Luke 24: 25-27)
When we see Jesus as our righteousness (1 Corinthians 1: 30), as the One who helps us in all our need (Philipians 4: 13, 19), then we grow and flourish:
"The righteous shall flourish like the palm tree: he shall grow like a cedar in Lebanon." (Psalm 92: 12)
"Palm tree" is a picture of righteousness that we receive as a gift, as opposed to earning it through our merits. This type is confirmed in the story of Tamar, the daughter-in-law of Judah who deceived her father-in-law Judah to impregnate her. When she confronted him as the father, and as the one who refused to release his sons to bear her a child, Judah admitted:
"And Judah acknowledged them, and said, She hath been more righteous than I; because that I gave her not to Shelah my son. And he knew her again no more." (Genesis 38: 26)
Imagine that -- Tamar was righteous and Judah was not.
Whe we approach God as Father and in our effort, that displease Him. When we approach God as the one who has helped us, who makes us righteous, then our works, our sacrifices, please Him. Let us not see God as a Father whom we serve in our own effort, but rather let us see the Son, and Let Him make us righteous.