Why is it the atheist/humanist speaks with so much more confidence and authority about his faith than the Lord's Disciples?
Could it be because he knows the object of his faith (himself) so much better than we know ours?
He speaks from deep knowledge and vast experience, while we stumble along, trying to get by with imagination, shallow book facts, and vague hope.
We must learn to know our Savior intimately and without distraction. We must know Him as well as we know ourselves, and then live and speak and think accordingly.
Because, where is the glory for God when our testimony begins with, "Well, I believe that..."?
Let's be honest. When we use it like this, "I believe" is not a statement of doctrine, but a confession of how thoroughly we lack true, life-changing knowledge. It justifies the unbelief of unbelievers, and gives doubters ample room to doubt.