It seems unfair. We have grown too used to the grace of God. Your goal in this lesson is to impress on your students the Holiness of God. If you do it well, if you teach as R.C. Sproul and Jerry Bridges did for me, your student's lives will never be the same. How many attributes of God can we recall.
Mercy is one.
As we read this passage, look for how Aaron's sons died. Someone describe Aaron's clothes. Verses 24 says the people shouted for joy and fell facedown. Aaron's son are prohibited from drinking. Let's skip back up to the section where Aaron's kids die.