In this sentence the author to say "before we decide a. We must find out the truth and open mind, a particular selection of items or to decide not just what to listen to, just once, "he said.
In this sentence, the author wants to say. "Before we judge the matter. We must find the truth and an open mind. Where we do not choose or decide just what is heard only once. "
In this sentence the author want to say "Before we judge a particular subject. We need to find the truth and keep your mind wide open. We do not choose or decide just what I've heard only once. "