Not Every Righteous or Well-Mannered Man Is Suitable For Leadership Or to Be Placed In a Position of Authority

Shaikhul Islaam Ibn Taymiyyah (rahimahullaah) stated whilst discussing the subject matter of Imtihaan (i.e. testing):

And likewise, when he (i.e. a person) desires to give someone a position of authority, he tests him (imtahanahu), just as Umar Ibn Abdul Azeez commanded his servant to test Ibn Abee Moosaa (yamtahinahu) when his mannerism amazed him (somewhat), so he said to him, “You know of my position with the Ameer ul-Mumineen, so how much will you give me if I indicate (the appropriateness) of your (being given) authority to him? So he gave him a great amount of wealth. And from this Umar knew that he was not fit for authority.

http://www.thenoblequran.com/sps/sp.cfm?subsecID=BDH05&articleID=BDH050015&articlePages=1