Tauhid is: Insulting God alone in worship and not associating with Him. And this is the teaching of all Rasul alaihimusshalatuwassalam. Even monotheism is the principal that is built upon it all teachings, so if this subject does not exist, deeds deeds become useless and fall, for it is illegitimate a worship without tauhid.
Question: Is there a perfect human being? Answer: There is no perfect human being, because everyone has a weakness. Someone who believes, must have mistakes and has a bad nature that is difficult to remove. No pure or perfect believer.