The phrase “Thin places” seems to have its roots in ancient (not Celtic) Irish spirituality and mysticism. It is a place where heaven and earth meet. A physical place where the boundary between heaven and earth “is thin.”
Why are they thin?
• These are not just places where we go to get a spiritual high, to fill up the gas tank of my soul. It’s not merely a feel-good place.
• It’s a doorway, a threshold. Seemingly simple, it is a place and an encounter that lead to a bigger, wider, unexpected, more glorious place. (Like the plain entrance door that leads into the Sistine Chapel)
• It is a place of light, where we encounter wisdom, and insight, and acceptance and healing.
• It is a place of darkness, where we encounter the risen Jesus who asks the question “And who do YOU say that I am? Do you understand and believe that:
o I can make you aware?
o I can answer the question?
o I can heal you of that temptation that pulls the destructive trigger in your life?
o I can forgive you when you fail?
It is a place where we are jolted out of our old ways of seeing the world. When you live here, you live life on the edge; you have to be taught how to live there. You don’t do this alone. Notice that in the First Reading of this week’s Scripture for Mass, TWO people received the blessing. Jesus talks about “When two (or three) are gathered…” (Matthew 18:20). Jesus “…sent them out ‘in twos.'” (Mark 6:7)
Some questions to ponder:
• When was the last time you were at a “thin place?’ Where was it?
• Who was your companion?
• What happened?
• Is the Lord calling you to re-visit that place now?
• Is the Lord calling you to visit someplace new that is a “thin place?
• How will you respond?
Fr. Charles Zlock 
I believe thin places are inherently thin - the eternal world and the present world is knitted tightly together. Though God is present everywhere and is the same yesterday, today and forever, thin places are places where we listen better. WE are changed by entering them. It is so much easier to pray in thin places.
Thank you for you lovely post.
Glad you enjoyed it. I actually recently discovered the phrase, did some research and used it as the basis of a homily at a retreat for people in recovery. It seemed to have a positive impact. I liked your phrase, “We are changed by entering them.” And yes, some thin places are locales where it is, indeed, easier to pray. Several retreat houses I have visited and certain places in nature and where I go to unwind and relax are like that. Gracie for the kind words. Fr. Zlock