The Christian Belief ''Dogma'' of ''The Mysteries of Faith'' - can trace it's origina as far back as The Ancient Greek and related ''Pagan'' Beliefs. In short, the term related to ''what'' a Person is taken to Believe on ''Faith of Belief'' rather than actual, physical evidence. The belief ''explains'' how a Faithful (Believer) need not always ''accept'' what ''cannot be explained''. Many Theologians thru the Centuries had clung to ''Mystery of Faith'' as the principle explaination of the many ''Supernatural'' or ''Preturnatural'' phenomenon (often well documented or not), which occur throughout a ''Believers'' Religious System.
By way of example, using The Catholic Church - such examples of ''Mystery of Faith'' is best attributed to The Holy Eucharist, or in particular point - The ''Last Supper''. During the Daily ''Ritual'', a Priest (or other Ordained Holy Person), presents a Bread Wafer (or similar subsititue, depending) - to The Faithful (Congregation). By invoking a ''verbal description'' of Jesus Christ's ''Last Supper'' (before His eventual capture and execution), The Wafer is raised for view. By invoking the phrase of ''The Mysteries of Faith'', a Believer is led to assume that the ''impending'' Transfiguration (which has previosuly been discussed) - is ''Supernaturally'' transformed froma simple ''Wafer'' into the ''actual'' ''flesh of Christ'' (at least by Belief). It is this ''specimein'' which will eventually be ''consumed'' in keeping with The Book of 1st Corinthians (which mentions Christ saying to His Disciples....''Do This In Memory of Me'').
Often decried by those wh either do NOT believe or are of another Belief System, ''Mysteries of Faith'' have been used to justfy other Dogmas such as ''Popular Piety'' or a Belief System based in such things as healing or curative properties found in many ''Holy Relics'' (bone, personal items or clothing etc). The Belief in such items go back well into the 9th Century AD (for Christians) and even farther among Paganistic Belief Systems (or even non-Christain Religions). Most Religious Systems use such a Belief as a reference point for Self Belief and often cite such for explaination.