Here is, I. The great sin that Nadab and Abihu were guilty of: and a great sin we must call it, how little soever it appears in our eye, because it is evident by the punishment of it that it was highly provoking to the God of heaven, whose judgment, we are sure, is according to truth. But what was their sin? All the account here given of it is that they offered strange fire before the Lord, which he commanded them not (Lev 10:1), and the same Num 3:4. 1. It does not appear the they had any orders to burn incense at all at this time. It is true their consecration was completed the day before, and it was part of their work, as priests, to serve at the altar of incense; but, it should seem, the whole service of this solemn day of inauguration was to be performed by Aaron himself, for he slew the sacrifices (Lev 9:8, Lev 9:15, Lev 9:18), and his sons were only to attend him (Lev 10:9, Lev 10:12, Lev 10:18); therefore Moses and Aaron only went into the tabernacle, v. 23. But Nadab and Abihu were so proud of the honour they were newly advanced to, and so ambitious of doing the highest and most honourable part of their work immediately, that though the service of this day was extraordinary, and done by particular direction from Moses, yet without receiving orders, or so much as asking leave from him, they took their censers, and they would enter into the tabernacle, at the door of which they thought they had attended long enough, and would burn incense. And then their offering strange fire is the same with offering strange incense, which is expressly forbidden, Exo 30:9. Moses, we may suppose, had the custody of the incense which was prepared for this purpose (Exo 39:38), and they, doing this without his leave, had none of the incense which should have been offered, but common incense, so that the smoke of their incense came from a strange fire. God had indeed required the priests to burn incense, but, at this time, it was what he commanded them not; and so their crime was like that of Uzziah the king, Ch2 26:16. The priests were to burn incense only when it was their lot (Luk 1:9), and, at this time, it was not theirs. 2. Presuming thus to burn incense of their own without order, no marvel that they made a further blunder, and instead of taking of the fire from the altar, which was newly kindled from before the Lord and which henceforward must be used in offering both sacrifice and incense (Rev 8:5), they took common fire, probably from that with which the flesh of the peace-offerings was boiled, and this they made use of in burning incense; not being holy fire, it is called strange fire; and, though not expressly forbidden, it was crime enough that God commanded it not. For (as bishop Hall well observes here) "It is a dangerous thing, in the service of God, to decline from his own institutions; we have to do with a God who is wise to prescribe his own worship, just to require what he has prescribed, and powerful to revenge what he has not prescribed." 3. Incense was always to be burned by only one priest at a time, but here they would both go in together to do it. 4. They did it rashly, and with precipitation. They snatched their censers, so some read it, in a light careless way, without due reverence and seriousness: when all the people fell upon their faces, before the glory of the Lord, they thought the dignity of their office was such as to exempt them from such abasements. The familiarity they were admitted to bred a contempt of the divine Majesty; and now that they were priests they thought they might do what they pleased. 5. There is reason to suspect that they were drunk when they did it, because of the law which was given upon this occasion, Lev 10:8. They had been feasting upon the peace-offerings, and the drink-offerings that attended them, and so their heads were light, or, at least, their hearts were merry with wine; they drank and forgot the law (Pro 31:5) and were guilty of this fatal miscarriage. 6. No doubt it was done presumptuously; for, if it had been done through ignorance, they would have been allowed the benefit of the law lately made, even for the priests, that they should bring a sin-offering, Lev 4:2, Lev 4:3. But the soul that doth aught presumptuously, and in contempt of God's majesty, authority, and justice, that soul shall be cut of, Num 15:30.

II.The dreadful punishment of this sin: There went out fire from the Lord, and devoured them, Lev 10:2. This fire which consumed the sacrifices came the same way with that which had consumed the sacrifices (Lev 9:24), which showed what justice would have done to all the guilty people if infinite mercy had not found and accepted a ransom; and, if that fire struck such an awe upon the people, much more would this.

1.Observe the severity of their punishment. (1.) They died. Might it not have sufficed if they had been only struck with a leprosy, as Uzziah, or struck dumb, as Zechariah, and both by the altar of incense? No; they were both struck dead. The wages of this sin was death. (2.) They died suddenly, in the very act of their sin, and had not time so much as to cry, "Lord, have mercy upon us!" Though God is long-suffering to us-ward, yet sometimes he makes quick work with sinners; sentence is executed speedily: presumptuous sinners bring upon themselves a swift destruction, and are justly denied even space to repent. (3.) They died before the Lord; that is, before the veil that covered the mercy-seat; for even mercy itself will not suffer its own glory to be affronted. Those that sinned before the Lord died before him. Damned sinners are said to be tormented in the presence of the Lamb, intimating that he does not interpose on their behalf, Rev 14:10. (4.) They died by fire, as by fire they sinned. They slighted the fire that came from before the Lord to consume the sacrifices, and thought other fire would do every jot as well; and now God justly made them feel the power of that fire which they did not reverence. Thus those that hate to be refined by the fire of divine grace will undoubtedly be ruined by the fire of divine wrath. The fire did not burn them to ashes, as it had done the sacrifices, nor so much as singe their coats (Lev 10:5), but, like lightning, struck them dead in an instant; by these different effects of the same fire God would show that it was no common fire, but kindled by the breath of the Almighty, Isa 30:23. (5.) It is twice taken notice of in scripture that they died childless, Num 3:4, and Ch1 24:2. By their presumption they had reproached God's name, and God justly blotted out their names, and laid that honour in the dust which they were proud of.

2.But why did the Lord deal thus severely with them? Were they not the sons of Aaron, the saint of the Lord, nephews to Moses, the great favourite of heaven? Was not the holy anointing oil sprinkled upon them, as men whom God had set apart for himself? Had they not diligently attended during the seven days of their consecration, and kept the charge of the Lord, and might not that atone for this rashness? Would it not excuse them that they were young men, as yet unexperienced in these services, that it was the first offence, and done in a transport of joy for their elevation? And besides, never could men be worse spared: a great deal of work was now lately cut out for the priests to do, and the priesthood was confined to Aaron and his seed; he has but four sons; if two of them die, there will not be hands enough to do the service of the tabernacle; if they die childless, the house of Aaron will become weak and little, and the priesthood will be in danger of being lost for want of heirs. But none of all these considerations shall serve either to excuse the offence or bring off the offenders. For, (1.) The sin was greatly aggravated. It was a manifest contempt of Moses, and the divine law that was given by Moses. Hitherto it had been expressly observed concerning every thing that was done that they did it as the Lord commanded Moses, in opposition to which it is here said they did that which the Lord commanded them not, but they did it of their own heads. God was now teaching his people obedience, and to do every thing by rule, as becomes servants; for priests therefore to break rules and disobey was such a provocation as must by no means go unpunished. Their character made their sin more exceedingly sinful. For the sons of Aaron, his eldest sons, whom God had chosen to be immediate attendants upon him, for them to be guilty of such a piece of presumption, it cannot be suffered. There was in their sin a contempt of God's glory, which had now newly appeared in fire, as if that fire were needless, they had as good of their own before. (2.) Their punishment was a piece of necessary justice, now at the first settling of the ceremonial institutions. It is often threatened in the law that such and such offenders should be cut off from the people; and here God explained the threatening with a witness. Now that the laws concerning sacrifices were newly made, lest any should be tempted to think lightly of them because they descended to many circumstances which seemed very minute, these that were the first transgressors were thus punished, for warning to others, and to show how jealous God is in the matters of his worship. Thus he magnified the law and made it honourable; and let his priests know that the caution which so often occurs in the laws concerning them, that they must do so that they die not, was not a mere bugbear, but fair warning of their danger, if they did the work of the Lord negligently. And no doubt this exemplary piece of justice at first prevented many irregularities afterwards. Thus Ananias and Sapphira were punished, when they presumed to lie to the Holy Ghost, that newly-descended fire. (3.) As the people's falling into idolatry, presently after the moral law was given, shows the weakness of the law and its insufficiency to take away sin, so the sin and punishment of these priests show the imperfection of that priesthood from the very beginning, and its inability to shelter any from the fire of God's wrath otherwise than as it was typical of Christ's priesthood, in the execution of which there never was, nor can be, any irregularity, or false step taken.

And Nadab and Abihu - took either of them his censer - The manner of burning incense in the temple service was, according to the Jews, as follows: -

"One went and gathered the ashes from off the altar into a golden vessel, a second brought a vessel full of incense, and a third brought a censer with fire, and put coals on the altar, and he whose office it was to burn the incense strewed it on the fire at the command of the governor. At the same time all the people went out of the temple from between the porch and the altar. Each day they burned the weight of a hundred denaries of incense, fifty in the morning, and fifty in the evening. The hundred denaries weighed fifty shekels of the sanctuary, each shekel weighing three hundred and twenty barleycorns; and when the priest had burned the incense, he bowed himself down and went his way out. See Maimonides' Treatise of the Daily Service, chap. iii. So when Zacharias, as his lot fell, burned incense in the temple, the whole multitude of the people were without at prayer while the incense was burning, Luk 1:9, Luk 1:10. By this service God taught them that the prayers of his faithful people are pleasing to him, whilst our High Priest, Christ Jesus, by his mediation puts incense to their prayers; (see Psa 141:2; Rom 8:34; Heb 8:1, Heb 8:2; Heb 9:24; Rev 8:3, Rev 8:4); for the priests under the law served unto the example and shadow of heavenly things; Heb 8:5." See Ainsworth in loco.

In the preceding chapter we have seen how God intended that every part of his service should be conducted; and that every sacrifice might be acceptable to him, he sent his own fire as the emblem of his presence, and the means of consuming the sacrifice - Here we find Aaron's sons neglecting the Divine ordinance, and offering incense with strange, that is, common fire, - fire not of a celestial origin; and therefore the fire of God consumed them. So that very fire which, if properly applied, would have sanctified and consumed their gift, became now the very instrument of their destruction! How true is the saying, The Lord is a consuming fire! He will either hallow or destroy us: he will purify our souls by the influence of his Spirit, or consume them with the breath of his mouth! The tree which is properly planted in a good soil is nourished by the genial influences of the sun: pluck it up from its roots, and the sun which was the cause of its vegetative life and perfection now dries up its juices, decomposes its parts, and causes it to moulder into dust. Thus must it be done to those who grieve and do despite to the Spirit of God. Reader, hast thou this heavenly fire? Hear then the voice of God, Quench not the Spirit. Some critics are of opinion that the fire used by the sons of Aaron was the sacred fire, and that it is only called strange from the manner of placing the incense on it. I cannot see the force of this opinion.

Which he commanded them not - Every part of the religion of God is Divine. He alone knew what he designed by its rites and ceremonies, for that which they prefigured - the whole economy of redemption by Christ - was conceived in his own mind, and was out of the reach of human wisdom and conjecture. He therefore who altered any part of this representative system, who omitted or added any thing, assumed a prerogative which belonged to God alone, and was certainly guilty of a very high offense against the wisdom, justice, and righteousness of his Maker. This appears to have been the sin of Nadab and Abihu, and this at once shows the reason why they were so severely punished. The most awful judgments are threatened against those who either add to, or take away from, the declarations of God. See Deu 4:2; Pro 30:6; and Rev 22:18, Rev 22:19.

And there went out fire from the Lord,.... They sinned by fire, and they were punished by fire, either from heaven, or from the most holy place, where the Lord dwelt between the cherubim; this was of the nature of lightning, as appears by what follows:

and devoured them; not reduced them to ashes, for neither their bodies nor their clothes were burnt with this fire, as is clear from Lev 10:4 but their lives were destroyed, they were lifeless, their souls were separated from their bodies by it, and they died; which is often the case by the lightning, that the clothes of those who are killed with it are untouched, and scarce any marks of violence on their bodies; and so the Targum of Jonathan says of these, their bodies were not burnt:

and they died before the Lord; upon the spot where they were offering incense, in the holy place, over against the most holy place. This was very awful, like the case of Ananias and Sapphira, and may seem severe: it was for the terror of others in the priesthood, or who should come after, to take care that they performed their office according to the divine precepts, and brought in no innovation into their service. And when it is considered that these were the sons of the high priest, newly invested with an high and honourable office, and just had the laws of the priesthood delivered unto them, and yet deviated from them as soon as in their office, and very probably, from what follows, went drunk into their service, their sin will appear aggravated, and the punishment less severe. This shows there is nothing in carnal descent, these were the sons of Aaron the high priest, that acted this part, and came to this end; the proneness of men to transgress the laws of God as soon as given them; thus the people of Israel fell into idolatry as soon as the moral law was given; and here the priests, as soon as the ceremonial laws, relating to the priesthood, were delivered to them; and also that the law made sinful men priests, and that the Levitical priesthood was imperfect; and that no order of men are free from sin, or exempt from punishment: and the whole of the divine conduct in this affair may lead us to observe how jealous God is in matters of worship; how much he dislikes hypocrites, and formal professors; how severe he will be against such who bring in strange doctrines; what will be the fate of the contemners of Gospel doctrines and ordinances; and how much he resents those who trust in themselves, and their works, and bring in anything of their own in the business of salvation, which is strange fire, sparks of their own kindling, a burning incense to their own drag, and sacrificing to their own net.

there went out fire from the Lord, and devoured them--rather, "killed them"; for it appears (Lev 10:5) that neither their bodies nor their robes were consumed. The expression, "from the Lord," indicates that this fire issued from the most holy place. In the destruction of these two young priests by the infliction of an awful judgment, the wisdom of God observed the same course, in repressing the first instance of contempt for sacred things, as he did at the commencement of the Christian dispensation (Act 5:1-11).