I think that when a Christian frowns at or objects to the mystical, they are forgetting that all christians are mystics.
I was raised in an liturgical church where most of our prayers were read out from the Book of Common Prayer or some other service book. Personal prayer was done in silence and no one ever taught me to pray out loud.
Then, after receiving Christ, I was taught the mechanics of prayer by way of the ACTS model:
Adoration Confession Thanksgiving Supplication
That gave me a framework of how to pray. Yet there was still that something that was missing.
Not too long later, I was introduced charismatic revival and began to speak in tongues. It was during this time that an oomph! was added to my prayer life. I was also told (and not formally taught) that when we didn't know what to pray we should pray in tongues.
At the same time, I was taught that prayer is like a conversation/talking with God. Yet most of the time it seem more like a monologue with us presenting a long shopping list to God. if talking with God was a dialogue then how do we hear him. I was taught that He speaks to us through the bible, His Word. Doesn't he speak to us directly like Paul and Peter?
All this time, I have had a attraction to the medieval and with my renewed faith, medieval christianity. The monks like Francis of Assisi and Brother Lawrence in particular. I was drawn to the life of contemplation. I wanted to learn meditation but the westernize christian traditions which I was brought up and trained by may frown at the mention of the word.
What's more, these past couple of years, my church has been going into the whole soaking in the Lord thingie. Which a pastor friend called a "fad." Truth be told it's actually waiting on the Lord for Him for a "download" aka meditation. However, I suspect if you were to use meditate instead of "soaking," there will be an adverse reaction from the anglicized modernist christians in the asian church. Those have forgotten that Christianity is from Israel which is in the Near East or West Asia.
Much of the reaction to meditation is because it is very much associated with Buddhism or Hinduism; and also related to going into a trance.
Bottom line: A mystic is someone who believes in the existence of a reality beyond the physical realm. Christians believe that in an existence beyond the physical or nature. Therefore, a christian is a mystic.
A Christian who does not believe in the supra-natural (I prefer this term over supernatural) is oxymoronic: believing in God and not believe in that which is above and beyond the natural. They must as well not pray. For prayer is the one activity in which a christian reaches out from the nature into the mystical. If you don't believe in the mystical then why bother to pray.