Just Sitting Down Quietly
You have seen the heart of the matter. This "just sitting down quietly" is the practice of the Way itself, brought to life in the stillness of your own being.
It is not an act of prayer, but a ceasing of all acting. It is the living embodiment of The Way of Non-Preference.
When you sit, you let go of "longing and aversion." You do not long for a "peaceful" sit or have an aversion to the "distracting" sound of the world outside. You do not judge the thought as "holy" or "impure." You do not prefer the feeling of "release" over the "pain in the shoulder."
As it is said, "Make the smallest distinction, however, and you are as far from it as heaven is from earth." In just sitting, you close that distance. You "hold no opinions for or against anything." The ache in your body, the memory that surfaces, the sound of the wind—these are not "good" or "bad." They are simply what is. By "just allowing" them, you cease to feed the "disease of the mind," which is like and dislike.
This is how you find The Inner Kingdom. You are not "doing" anything to earn it. You are not striving, or building, or even seeking. In that quiet, you become "poor in spirit"—empty of preference, empty of striving. And in that very moment, "theirs is the kingdom of heaven."
You are not laying up treasures on earth—not even the treasure of a "good prayer" or a "profound insight." You are simply being with your own heart. And "where your treasure is, there your heart will be also." In the sitting, your heart is the treasure. You become the "pure in heart," not by effort, but by allowing all things to be as they are. And in that purity, you "see God"—not as a distant being, but as the very presence, the very "light" and "Spirit" that you feel flowing through all things, including yourself.
And as you've found, this leads Beyond Words. The experience of "The presence" is not a concept. It is not an argument. It is "everywhere always right before your eyes," especially when the eyes are closed and the mind is still. You cannot "grasp the ungraspable," so you simply sit, and in that open-handed stillness, you are held by it.
When to practice? Your own spirit has given you the truest answer. The eagle does not consult a schedule to know when to soar or when to rest upon the cliff. It rests. The fox is still. The storms and the quiet pleasures of life are the only calls you need. When the world pulls you into a thousand distinctions, the heart remembers the Way of oneness. When the mind is lost in confusion, the spirit calls you to simply sit.
Do this. Sit. Allow. Let go. And see what is always there.