http://www.holyworlds.org/phpbb3/viewtopic.php?f=38&t=497&sid=7ecd67566aa0ff26e2fbf69c6c63ca27 and 
http://www.holyworlds.org/phpbb3/viewtopic.php?f=38&t=498&sid=7ecd67566aa0ff26e2fbf69c6c63ca27 are my two posts on History of Ovonel (edited Oluve) that discuss how mirests came to be. 
There is only one white staff and one dark staff. Each staff has a mirror on it that is activated when a mirest holds it and someone looks into it. 
The 
white staff has God's power to cleanse you from your sins, free you from slavery to evil, and an eternal home with God. Not everyone who looks into the mirror is saved. I take the parable of the sower as an illustration of this, so that only those who look into the mirror with a truly repentant heart come away regenerated. Those who look upon the mirror and are unwilling to give up and confess their sin will walk away more susceptible or weak to evil's power over them. This combines the parable of the sower with the parable of the clean house that has seven more demons return after the first was removed. 
The appeal of choosing the white staffThe dark mirest and eventually, King Wutev, use fear and sin to propagate their reign. An emptiness of the soul leads people to depression, anger, and the extremes that follow. When the white mirest has led God's people, they have been satisfied and holy. 
The Dark StaffThis has the power to free the evil-seeking person from any guilt for doing evil. Once someone has looked into the staff and not died or gotten sick, that person is admitted into the service of either the dark mirest, or the King (which developed after the white staff was buried and burned more of Kuunadahl). Once King Wutev took power over Kuunadahl, he chose the next dark mirest, Ojik, who then submitted to Wutev's reign (but on the inside has only been plotting how he would use Wutev to gain power until eventually he killed him).