In order to judge mankind with empathy, Jehovah has selected judges who themselves were men.
But, these are special men. The anointed are men who, although weak, sinful and imperfect overcame
these obstacles and lived to glorify Jehovah and died faithful to the end.
To be judged by such persons would give no other humans cause to complain that their judge didn't know what it was like
to be faced with tough times.
These "kings and priests" were "bought" with Jesus' blood. He selects them personally because Jesus is well-acquainted with human misery
and pain and a martyrs death.
These "kings" will rule with knowledge and experience of humanity at its core identity thus serving human needs in a way a spirit king without such
intimate knowledge would be less qualified.
Bottom line? Jehovah wants to be a FAIR judge and He does this by stepping out of the way and letting experienced magistrates do the job.