4. IF GOD DOES NOT AUTHORIZE SOMETHING, LEAVE IT ALONE.
Leviticus 10:1,2 - "Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it, put incense on it, and offered profane fire before the LORD, which he had not commanded them. So fire went out from the LORD and devoured them, and they died before the LORD."
Their actions here were not approved by God. They did not have His authority to do what they did. They should not have gone beyond the instructions God had provided them. Today, there are many opportunities to be involved in things that are simply not authorized by the New Testament (cf. Col. 3:17). The safe course is to abstain from such practices, remembering we are here to please God, not self (cf. Col. 1:9,10). To engage in that what God has neither explicitly forbidden nor authorized in any way (either generically or specifically) is foolish. If you don't leave it alone, you risk God's displeasure and your own destruction. Furthermore, if one is willing to go beyond God's authority in one area, what will stop him from doing the same in other areas (cf. Gal. 1:6-10)?
5. GOD DOES NOT ACCEPT JUST ANY TYPE OF WORSHIP.
This is another lesson from Leviticus 10:1,2.
Some might speculate that any worship a real priest of God offered would be graciously accepted by the Most High. That is simply not true. These were men of God but they worshiped in a way that God had not commanded. The LORD did not accept their worship modification. What makes us think He will accept our modifications today from the New Testament pattern which He has revealed?
6. THAT WHICH MAN CONSIDERS TO BE SMALL & INSIGNIFICANT IS NOT NECESSARILY SUCH TO GOD.
This is yet another lesson from Leviticus 10:1,2.
From a human perspective, some might suggest that it was rather harsh for these priests to forfeit their lives for merely engaging in that which God had not commanded, but the offense was obviously serious to God (and therefore it should be to us as well). We are not in a position to determine what is or isn't important to God based upon our personal preferences. We are not equals with Jehovah! God's ways and thoughts are far above our own (cf. Isa. 55:8,9). We cannot read God's mind and therefore must remember our proper place as servants. Let us do His will and not go beyond it, even when we think a minor change or modification would not be a "big deal."
7. OUR RELATIONSHIP WITH GOD IS MORE IMPORTANT THAN ANY HUMAN RELATIONSHIP.
Leviticus 10:3,6 - "And Moses said to Aaron, 'This is what the LORD spoke, saying: "By those who come near Me I must be regarded as holy; and before all the people I must be glorified."'...And Moses said to Aaron, and to Eleazar and Ithamar, his sons, 'Do not uncover your heads nor tear your clothes, lest you die, and wrath come upon all the people. But let your brethren, the whole house of Israel, bewail the burning which the LORD has kindled.'"
The father and brothers of the two priests who were struck down by God were not allowed to mourn for their loss. The deaths of these two men were deserved and administered by the LORD himself. We today must love God more than family, even when it really hurts! Our relationship with our Creator must supersede any and all human relationships. I know of an elder who lead a congregation to withdraw from his son who had embraced sin and would not repent. He loved his son, but he loved the Lord more (cf. Luke 14:26).