One thing we know about Jesus is that he was very good at using rhetorics. Other than the accounts in several books about him using rhetorical techniques very advanced for the day, there's also evidence that he was skilled enough to start a religion. But any information finer than that is hard to prove. The books are over a thousand years old, written at different times by different people, followed by several translations, so we can't know his exact word choice or style of speech with certainty. The closest to the 'source' are ancient Greek texts which were likely translated from some other language.