To be spiritual means to somehow transcend the physical. In terms of our experience, “physical” fundamentally means the body. The most intimate physicality in existence for you is your body; and this body is just a piece of earth. So one instrument or method for a person to transcend the physical is to constantly remind the physical – experientially, not intellectually – of what it really is.
Just sitting down cross-legged on the floor experientially reminds the body of this in some way because the moment the body is in touch with the earth, it knows it is earth. That is why spiritual people walk barefoot and always sit on the earth because the body should never forget what it is. If it forgets, it starts making fanciful demands. But if you constantly remind it, it is in its place.
Being in touch with the earth has many other aspects to it. Fundamentally, this whole body is just a play of five elements. Whether it is the individual human body or the larger cosmic body, essentially, they are made of the pancha bhutas or the five elements – earth, water, fire, air and space.
What you call as “myself” is just a mischief of these five elements. This elemental play happens in a different way when it is in touch with the earth. Every day, if for at least an hour, you stick your hands into the earth and do something with the ground, the body is reminded, not just intellectually, but in a very fundamental way. This reminder must be on all the time.
In a mountain, this reminder is happening in a very big way. A mountain is a place where earth has risen to reach out to you. If you make a hole in it or go into a cave, earth is on all sides; it is a big reminder. That is why, though the conditions are not comfortable, all spiritual beings generally move to the mountains. Mean sea level would be much more comfortable because you could live there with the bare minimum.
On the mountains, it is very difficult. But still they choose mountains because it gives you a closer contact with the earth. It is a constant reminder for the body, that the play of elements in the earth and the play of elements in this body are not different.