Speaking to the Hebrew believers, the author (who we believe was Paul) said he had much more to say about Jesus being their High Priest in the order of Melchizedek. Still, it was difficult to explain because they were 'spiritually dull' and didn't seem to listen. They had been believers long enough that they ought to have taught others. But instead, they needed someone to teach them again the basic things about God's word. You "become such as need milk and not of strong meat" (Hebrews 5:12). Paul was NOT talking about doctrines. He emphasized discipleship. Having all our doctrines right is meaningless if we do not apply God's word to live a holy lifestyle pleasing Him.