To accept an interpretation of life upon authority is permissible only if we have looked into the foundations of the authority we accept. But if we must determine the foundations of the authority, we no longer accept authority on authority. Authority could be authority to us only if we already knew that it had the right to claim authority. Such could be the case only if we knew in advance the nature of that authority. Thus we would have a theory of being already taken for granted at the outset of our investigation.

Greg Bahnsen, Van Til’s Apologetic, Pg. 95-96

After Jesus Christ we have no need of speculation, after the gospel no need of research. When we come to believe, we have no desire to believe anything else; for we begin by believing that there is nothing else which we have to believe…My first principle is this. Christ laid down one definite system of truth which the world must believe without qualification, and which we must seek precisely in order to believe it when we find it…What you must seek is what Christ has taught, and precisely as long as you are not finding, precisely until then, you must go on seeking until you do find it.

Tertullian, Prescription against Heretics