v1-3: Testing the words of the prophet; the Lord allows such things to test His people. The occurrence of a miracle does not make something false be true. The message is the test, not the miracle. It is unsafe to give credence to a message solely because it is accompanied by a miracle; compare Acts 8.9.
Beware the new message "other gods you have not known"; see Acts 17.21.
v4: The best way to avoid being led astray is to stick close to the Lord. That was true for the Israelite, and is true for the Christian.
v5: The man who promoted idolatry , and turned the people from following God, would be put to death, 2 Tim 3.5. Even though the Lord had tested His people, the man was responsible for his words, and would suffer the consequences.
v6-7: Temptation can be harder when it comes through someone close, but love for God must exceed even family ties. The word "entice" is used, implying subtlety, even deceit; the command is clear, that we must stick close to God, and be discerning.
v8-10 Even in this situation, there was no room for pity. Idolatry was something serious.
There may be a temptation to loyalty to the one who is close; but this cannot take precedence over idolatry.
v11: The public execution who stand as a warning to all Israel that idolatry was serious. The aim was that the people would not again fall into this sin.
v12-18: In the situation where there is a rumour of idolatry, the people had to investigate properly (v14); idolatry would be introduced by wicked men, not godly (v13). Once proven, the town, its inhabitants, and its animals, had to be destroyed (v15-16).
The implication is that the people had failed to identify the individual, and had failed to deal properly with the guilty one (as in v1-3), and therefore they all shared the guilt.
Such action, in offering the whole town as a burnt offering to the Lord God, will turn away the Lord's fierce anger, and bring mercy and compassion. Here is obedience, even at a price; and there will be reward.
The lesson for the Christian is to ruthlessly deal with personal sin, knowing its power to damage our lives.