You could give a simple heading to chapters 8-9: “They did just as the LORD commanded.” Unfortunately, that same heading can not be given to chapter 10. Instead, the heading has to read, “Contrary to the LORD’s Command!” The text is not entirely clear what got into Nadab and Abihu (10:1-2), but like so many of us, they did their own thing. The result was serious. Instead of the presence of the LORD evidenced in flame to consume the sacrifice (chapter 9), the presence of the LORD bursts forth to consume the sinners. We could ask a thousand questions about this scene. We want to know why God dealt so seriously with these boys. Actually, I think that is just what God wants us to see in this story. Still, at this early stage in history, He wants all humanity to know just how serious sin is. We would later know the seriousness of sin by His willingness to empty Himself by becoming a man to die on a cross for the victory over that sin.
One other thing we ought to contrast in these three chapters. Notice the joy that obedience brings. Chapter 9 concludes with all the people rejoicing. However, notice the despair that disobedience brings. Such is still the case today. My special prayer today is for those of you dealing with the despair brought on by the disobedience of someone you deeply love.