Since the beginning of recorded time, and probably long before, there have been secret religious societies and mystery religions.  The difference between the two is that a mystery religion is a completely different religion or church while a secret society is usually a group that operates somewhat in secret within a major public church.
    Secret societies may be completely secret, that is, even the existence of the group is a secret, while with others, the group is well known, but the teachings and ceremonies are secret.  Some well known spiritual or religious secret societies are the Rosicrucians and the Masons.
    In the case of mystery religions, the Therapeutae of Egypt, the Essenes and the Gnostic Christians can be included.  With these, and other mystery religions, there were basically two kinds of teachings, those that were spoken of publicly and those that were kept secret, shared only with other members of the church.  We know from the Bible and other historical documents from that time, that Jesus taught things to his apostles and a small group of disciples that were not shared with the public.  
    Unfortunately, because so many pre-Christian or pagan religions were mystery religions, many Christians today consider all such religions to be pagan and false, even those that accept secret societies as part of their church or other Christian churches.  Many don't think a church should have secrets.
    Their are reasons why a church, religion, or secret society keeps some things secret from a spiritual view point ( there are also political reasons that I won't get into).  First, as Jesus pointed out with the well known line, "Do not cast pearls before swine", trying to teach people something they are not ready to learn is a waste of time.  Also, some of the secret teachings can be harmful.  It may have been the discovery of some of these secrets without proper guidance that drove Van Gogh, Nietzsche and other less known individuals mad.  Such knowledge can also be used for evil.  Hitler and Roman emperor Nero are examples of some evil persons who discovered some spiritual truths and used them to do evil.