He stood between the dead and the living; and the plague, etc. - What the plague was we know not, but it seems to have begun at one part of the camp, and to have proceeded regularly onward; and Aaron went to the quarter where it was then prevailing, and stood with his atonement where it was now making its ravages, and the plague was stayed; but not before 14,700 had fallen victims to it, Numbers 16:49.

If Aaron the high priest, with his censer and incense, could disarm the wrath of an insulted, angry Deity, so that a guilty people, who deserved nothing but destruction, should be spared; how much more effectual may we expect the great atonement to be which was made by the Lord Jesus Christ, of whom Aaron was only the type! The sacrifices of living animals pointed out the death of Christ on the cross; the incense, his intercession. Through his death salvation is purchased for the world; by his intercession the offending children of men are spared. Hence St. Paul, Romans 5:10, says: If, while we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved Through His Life, i. e., by the prevalence of his continual intercession. 2 Corinthians 5:18, 2 Corinthians 5:19 : "And all things are of God, who hath reconciled us to himself by Jesus Christ, and hath given to us the ministry of reconciliation; to wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation." By the awful transactions recorded in this chapter, we may see how jealous God is of the sole right of appointing the way and means of salvation. Had any priesthood, and any kind of service, no matter how solemn and sincere, been equally available in the sight of Divine justice and mercy, God would not have resented in so awful a manner the attempts of Korah and his company in their new service. The way of God's own appointment, the agony and death of Christ, is the only way in which souls can be saved. His is the priesthood, and his is the only available sacrifice. All other modes and schemes of salvation are the inventions of men or devils, and will in the end prove ruinous to all those who trust in them. Reader, forget not the Lord who bought thee.

What the plague was we know not; but it seems from this to have begun at one part of the camp, and to have proceeded regularly onward.

Numbers 16:18,35 And they took every man his censer, and put fire in them, and laid incense thereon...

Numbers 25:8-11 And he went after the man of Israel into the tent, and thrust both of them through, the man of Israel, and the woman through her belly...

2 Samuel 24:16,17,25 And when the angel stretched out his hand on Jerusalem to destroy it, the LORD repented him of the evil...

1 Chronicles 21:26,27 And David built there an altar to the LORD, and offered burnt offerings and peace offerings, and called on the LORD...

1 Thessalonians 1:10 And to wait for his Son from heaven, whom he raised from the dead, even Jesus, which delivered us from the wrath to come.

1 Timothy 2:5,6 For there is one God, and one mediator between God and men, the man Christ Jesus...

Hebrews 7:24,25 But this man, because he continues ever, has an unchangeable priesthood...

James 5:16 Confess your faults one to another, and pray one for another, that you may be healed...

John 5:14 Afterward Jesus finds him in the temple, and said to him, Behold, you are made whole: sin no more, lest a worse thing come to you.

Conflict.
"Therefore let us also, seeing we are compassed about with so great a cloud of witnesses, lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us, looking unto Jesus the Author and Perfecter of our faith, who for the joy that was set before Him endured the Cross, despising shame, and hath sat down at the right hand of the throne of God. For consider Him that hath endured such gainsaying of sinners against themselves, that ye …
Thomas Charles Edwards—The Expositor's Bible: The Epistle to the Hebrews