'Perfection' in the Bible

Therefore leaving the teaching of the first principles of Christ, let us press on to perfection -- not laying again a foundation of repentance from dead works, of faith toward God,

Now if there was perfection through the Levitical priesthood (for under it the people have received the law), what further need was there for another priest to arise after the order of Melchizedek, and not be called after the order of Aaron?