The essence of this practice can be stated as a simple formula: ordinary experience plus mindfulness plus equanimity yields insight and purification. In this formula, each term is defined very precisely. Ordinary experience is defined as hearing, seeing, smelling, tasting, the feeling body and the thinking mind. Mindfulness is defined as specificity in awareness, clarity in awareness, continuity in awareness, richness in awareness, precision in awareness. Equanimity is defined as not interfering with the flow of the senses at any level, including the level of preconscious processing.
When sufficient mindfulness and equanimity are brought to bear on ordinary experience, we arrive at purification and insight. And, as a result of the purification and insight, our intrinsic happiness, our true birthright and spiritual reality, gets uncovered and we discover that what we thought was the world of phenomena—the world of time, space, and matter—turns out to really be a world of spiritual energy, and that we are in direct contact with it moment by moment. Because, when the senses become purified, when the inner conflicts—at all levels—have been broken up, the flow of these ordinary senses turns into a prayer, a mantra, a sacred song, and we find that, just by living our life, we are in moment-by-moment contact with the Source. In the Christian contemplative tradition this is called the "practice of the presence of God." In the Jewish mystical tradition it is called briah yesh me ayn—the experience of things (yesh) being continuously created (briah) from no-thing (ayn), that is, from God.
For most people the senses are opaque. A window is opaque if it is covered by soot; light can't come through. The soot is craving, aversion, and ignorance. When that's cleared away, the ordinary senses become literally transparent. It is very hard to describe what this is like. Hearing returns to being part of the effortless flow of nature, seeing returns to being part of the effortless flow of nature, and likewise with smelling, tasting, the body sensations whether they are pleasant, unpleasant, or neutral, they all go back to being part of "God's breath" so to speak.
Even the thinking process returns to being part of this effortless flow. At the beginning stages of meditation one is very concerned with overcoming the wandering thoughts in order to develop enough calm and concentration to be able to practice mindfulness. But when you get further along in the process there will be no necessity whatsoever to have a still mind because the ordinary flow of thought will be experienced as not different from the activity of the Source.