When you have investigated in this way until you have it thoroughly mastered, what happens next is what comes of its own accord. The mind is bound to converge in a big way; and the instant it converges, everything will appear to converge, being one and the same. The entire world will be nothing but elements.
How is this not the same as materialism?
It's not materialism, because with investigating that way, your mind first off will become very stillness, and if you will continue to investigate like this, your mind fill become very focused, and if all is good, one experiance will take place in you.
It's sure that the door that takes this way meditator is the body, something material, but the important point of this practice is mind, is concentration and awereness. So it's one very classic way, awereness and concentration that you must practice all day every day.
The most important point in this, is to turn your mind to liberation, like a boath in the middle of water must be turned to the beach all time, and so mind must be turned to liberation all the time. And if the mind have a right dirrection, you must just spread the sail of awereness on the mast of concentration, and the wind of kamma will do his job, so by awereness and concentration in all fenomena that you experiance in your daily life, after some period of right practice and right direction, you will step on something stable, save, a shelter of your mind, beyond the water, like a seilor who was burn a middle of ocean will steps on the beach...
So Ajahn Mun, just take his body like a support of his awereness and concentration, like we can take our daily life, or avery else. It's not much important, because truth is Truth, and this Truth is every where, in every dhamma you have all the Dhamma. We have all our life to choise our support of practice awereness and concentration, it's may be some thing material or not, something here or very far, it's not depends of that, it's depend of nothing, because is the thurth of freedom