The intrusion of evil into God’s creation was permitted by HIM as part of HIS profound and worthy purpose. It is hard to comprehend the wicked were made to serve God’s purpose but it is true.
They shall serve to manifest God’s inflexible justice in the infliction of retribution against unrepentant sinners. How could God be fully known were that not shown. Thus all shall serve, as it is written:
“God has made all things for HIMSELF. Yes even the wicked for the day of evil.” Proverbs 16:4
The devil, his angels and impenitent men shall all eventually be seen as vessels or servants, but vessels to dishonour not honour.
“Does not the potter have power over the clay, from the same lump to make one vessel for honour and another for dishonour.” Romans 9:21
If God had not allowed evil into His world how would we know the full extent of HIS character. HIS mercy, kindness, goodness, patience and above all HIS sacrificial love for us revealed at the Cross.