Jesusism - Just Another First Century Mystery Cult

[RoadRunner79]

There are 26 references in the NKJV to Christianity as a mystery religion in the New Testament.  

https://www.biblegateway.com/quicksearch...ultspp=250

I don't think that a search for the word mystery is a good way to make this determination.  You can look at "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life" and find the word "mystery" used a number of times.

I was looking at the origin of Mithraism in Rome the other day.  It seems that it's main strength as a movement came in the 2nd and 3rd centuries.  Most think it somehow came from the Persian version of Mithra, but are not sure how or exactly when; if it is a version of the Persian religion or a Roman religion, with Persian accents.  

Mithraism is known almost entirely from physical artifacts and dedicatory inscriptions. In total, over 400 archaeological find-spots related to Mithraism have been uncovered, along with about 1,000 dedicatory inscriptions and 1,150 pieces of sculpture.
There are very few contemporary written sources, and most of those that survive are outsider perspectives. References to Mithraism can be found in the following texts:

• Plutarch, Life of Pompey 24
  
• Porphyry, On the Cave of the Nymphs 6, 15-16, 17-18, 24-25
  
• Porphyry, On Abstinence from Animal Foods 4.16
  
• Tertullian (c.200), On the Soldier's Crown 15
  
• Origen (240s), Against Celsus 6.22
  

The lack of good written sources on Mithraism is largely due to its status as a mystery religion, in which the meaning of its iconography and rituals was a secret known only to initiates. Insiders did not record details of their religion and outsiders did not know much about it. This obviously makes things difficult for historians, so there is much about Mithraism that is still not known.
http://www.religionfacts.com/mithraism

So, in my view, the description of the mystery religions, is quite a bit different, from your googling the word "mystery" in the Bible (or in Darwin).

However, whether Christianity is accurately described by the term "mystery religion" has nothing to do with the claim that it was inspired by them.  For that they would need to make some sort of connection other than the vague unfalsifiable crap being put forth as history so far.  

It is one of those things, that may sound good on the surface but has little to support it.  Hence most respected historians do not ascribe to it, and it is held by internet amateurs and very few fringe scholars.