Micah's religion was what we call in Australia a "dog's breakfast" because from a biblical perspective it was an absolute mess. Micah embraced what many people still do today, imagining God would bless and benefit him because of his twisted efforts to honour Him. Because he did not know God, Micah did not walk in the way God laid forth in the Law of Moses. He made idolatrous images in violation of the law along with an ephod and consecrated one of his sons as his priest--until the Levite came along. Micah hired the drifter and grifter Levite, believing God would certainly do him good because he had a Levite as his priest (who was not a qualified priest at all!).
Micah was looking for God to do him good, and the Levite who wandered to find a place (and was treated like a son by Micah) was only too glad to take a better deal with the tribe of Dan after they stole Micah's gods. The men of Dan were pleased to steal Micah's idols and illegitimate "priest" after he had extended hospitality to them, and then they attacked Sidonians to take their land for themselves. Every person and group was out for their own interests without thought of others or God, and the heart of mankind has not changed at all. One of the best sermons I ever heard was taken from these scriptures, titled 10 Shekels and a Shirt by Paris Reidhead. He used this passage to point out the utilitarian appeal of a modern presentation of the Gospel that is like a Levite pretending to be priest--the offer of forgiveness without repentance, salvation without faith marked by obedience, and appeals to selfish motives rather than the glory of God simply because He is worthy.
How different things would have been if Micah had trusted and believed in the one true God Who is good! Instead of looking for a place the Levite could have been blessed to serve at the tabernacle where the presence of the LORD dwelt among His people. The tribe of Dan could have been content to receive their land by lot as an inheritance from God's hand, be satisfied in abundance, and give rather than steal. How different for the better we would be if we learned from their bad example! It is good for us to understand that in the worst examples in scripture we can catch glimpses of ourselves so we might repent of our sin and choose to do what pleases God. And if you haven't heard that sermon yet, it is well worth your time. Not only will it provide insight into Judges 17-18 but challenges all to examine our hearts so we might humble ourselves before God and by faith and obedience to be more like Jesus.