"Mystery" is not a word I often use even though I am a theologian. Indeed I avoid the word "mystery" because I am a theologian. To say that what Christians believe is mysterious invites the assumption that what we believe is not believable. In short, "mystery" suggests that what we believe defies reason and common sense. What we believe does defy reason and common sense; but yet I believe what Christians believe is the most reasonable and commonsense account we can have of the way things are.
"Mystery" does not name a puzzle that cannot be solved. Rather, "mystery" names that which we know, but the more we know, the more we are forced to rethink everything that we know.
Stanely Hauerwas, Cross-Shattered Christ: Meditations on the Seven Last Words, pp. 14-15.