That is the failings with Evanghelical Christianity.It fails to answer questions of common Christian sense.
1) So the reason we need a priesthood is?
Answer:
To keep us from jumping horses and throwing the first stone.
The first annointed priest was Aaron, brother of Moses, and he became priest because the Hebrews needed a buffer between them and the confused prophet. So Moses gave Aaron some teritory and proclaimed him a priest to conduct rituals on the behalf of the people. People needed a priest to moderate between a demanding prophet and their worldly views.

Just think what would have hapened ware not for Aaron with his judgement and mercy for his flock. either Moses would have been killed or the flock would have perished taking Moses's signs litteraly. Some stoning did occur, but it was prescribed only in times of crisis when crime itself was capital due to the precarious situation of the Hebrews. Adultery became a sin only after it lead to the loss of human life and the threating of another one. If the adulterers would have repented or gone to Moses than the whole episode wouldn't have occured.

Having a priesthood isn't like establishing a tyrany or establishing a status quo. Priests must exist so that the flock mentains its mundane pleasures while attaining salvation and the Kingdom of Heaven. The militant Orthodox Church of Romania has long abandoned quoting for the Bible to stop people having sex...and through work and discipline has managed to brace itself for the mesianic events of the 21st century, like poverty, corruption and deterirating health conditions among the general population.

Some brilliant Islamic judges have even gone as far as to create "sex marriage contracts" that allow the parties to enjoy sex without legal or moral consequences for either one of them.