“Now I know that the LORD will prosper me, because I have a Levite as priest" (v13). In this time, “everyone did what was right in their own eyes” (17:6), and the worship of God was mixed up with idol worship (syncretism). Instead of worshipping at the official tabernacle, Micah had a household shrine and idols, and he thought having his own Levite priest would give him supernatural power (v5). Instead, a group of Danites stole his priest and his idols (ch 18), symbolizing the spiritual chaos of the land.
“Inquire of God, please … “ (18:5). Thinking we can manipulate God to get what we want is magic, not Christianity. God calls us seek His glory, not our own.