Yeah, I have come to differentiate between "mysteries" and "mysticism," but this is my take on it. Paul talks about a mystery he was given.
Ephesians 3:1-6--For this reason, I, Paul, the prisoner of Christ Jesus on behalf of you Gentiles — you have heard, haven’t you, about the administration of God’s grace that He gave to me for you? The mystery was made known to me by revelation, as I have briefly written above. By reading this you are able to understand my insight about the mystery of the Messiah. This was not made known to people in other generations as it is now revealed to His holy apostles and prophets by the Spirit: The Gentiles are co-heirs, members of the same body, and partners of the promise in Christ Jesus through the gospel.
Paul also mentions the mystery of the union between a husband and wife being like Christ and the church in Ephesians 5. So, there are "Christian mystics" who base their beliefs on this verse.
The problem that I have with mysticism in general is that I believe the underlying premises is that we humans are divine or that we are God in some way. To me, this smacks of the original temptation where the serpent told Eve that she would be like God. I believe that we partake of the divine nature (2 Peter 1:4), but that we are not, and never will be, God in any way.
I'm probably opening a can of worms here, but this relates to the OP because the belief in human divinity is central to the teachings of Freemasonry. Hope this makes sense.