Said unto Aaron. Moses acted as God’s mouthpiece.
Take a censer. The Hebrew is definite, “Take the censer,” that is, the one Aaron used as high priest. Incense was a symbol of mediation and intercession (see Ps. 141:2; Rev. 8:3,4).
Unto the congregation. The incense was regularly offered only at the golden altar within the sanctuary. But now at God’s command Aaron carried it among the people without, thereby demonstrating his authority from God, and the power of God working in and through him.
An atonement. There was no time to choose and sacrifice an animal. Atonement was made by means of the incense in the censer, for the plague was already rampant among the people.