As I said in the beginning, what they did does not seem to the human mind as a sin deserving of death. It seems that they were sincere and had no evil intentions and they were obviously not expecting to die. But God sees their bringing fire “he had not commanded them” a thing which deserves the death sentence because it perverts His worship, which He is jealous for. By bringing strange and unauthorized fire before the Lord, Nadab and Abihu did not regard the Lord as holy, therefore, He brought immediate Judgment upon them, so that the people would know that God is jealous for His worship and He is not pleased with “strange fire.” Again, we have here the principle of “what is not commanded, is forbidden.”
It is proper here to observe how patient God actually is among us. We should not merely think because God does not bring immediate Judgment (upon the unregenerate) or discipline (upon His children) for worship which He has not authorized, that God is actually pleased with it. We should not take the patience of God as a sign of His approval of “strange fire…which he did not command them.” Rather, we should all the more and vigorously search the Scriptures to learn about the way in which God wants to be worshiped.
You Shall Not Add To It Or Take From It
Deut. 12:29-32 “When the LORD your God cuts off before you the nations whom you go in to dispossess, and you dispossess them and dwell in their land, 30 take care that you be not ensnared to follow them, after they have been destroyed before you, and that you do not inquire about their gods, saying, ‘How did these nations serve their gods?—that I also may do the same.’ 31 You shall not worship the LORD your God in that way, for every abominable thing that the LORD hates they have done for their gods, for they even burn their sons and their daughters in the fire to their gods. 32 “Everything that I command you, you shall be careful to do. You shall not add to it or take from it.
In warning Israel against idolatry, the Lord likewise commands them to follow His words only. They are to worship the LORD their God in the way that He has commanded them. They should not invent ways of worshiping God as the heathen did for their idols. Rather, the true worship of the true God is instituted by Himself alone. John Gill observes on this passage that we should “neither add any customs and rites of the Heathens to them, nor neglect anything enjoined on them”[10]. The command in v. 32 concerns especially the commandments concerning the worship of God. What is said is also applicable to all of God’s commandments, but especially in this context, to the way which God ought to be worshiped. The people of God should neither add to the worship of God, neither take away from the worship of God. Rather, they are to do everything that God’s commands us concerning His worship. Calvin notes on v. 32:
What thing soever I command. In this brief clause he teaches that no other service of God is lawful, except that of which He has testified His approval in His word, and that obedience is as it were the mother of piety; as if he had said that all modes of devotion are absurd and infected with superstition, which are not directed by this rule. Hence we gather, that in order to the keeping of the First Commandment, a knowledge of the true God is required, derived from His word, and mixed with faith. By forbidding the addition, or diminishing of anything, he pl...