But their writings, when collected, show no contradictions.

Paul does not disagree with Moses, John does not argue with David, etc., though they wrote on the most controversial subjects known to man. Instead, their teachings strengthen and support one another.
Some skeptics claim contradictions exist in the Bible, but ask them to produce one. Most will not even try! Usually they have never really studied the Bible, but are taking someone else's word about it. Proper study can reconcile any supposed contradictions that are suggested.