From a personal experience I think the models of knowing God in Judaism and in Christianity are different. If you are to be a disciple of Christ you must be humble to learn instruction from others. It is not proper to equate Paul's knowledge in Judaism to what he's yet to learn in Christ. As he obeys then he can start from there.
And Ananias had fear of the former Saul but both worked in obedience to fulfill the plan of God. I look forward to have that spirit of obedience to warn brothers where they are failing in their walk with God