The mind with it's positive, negative, neutral, disturbing, or joyful thoughts are always in flux. The thoughts seem to come from nowhere and are either happy, sad, elated, disturbing, or neutral. You often don't have control over what you are thinking. The thoughts seem to either come from nowhere or are triggered by a memory, anger, or jealousy. The Space in meditation behind all the thoughts is always unchanging. Like the ocean is always water but becomes a large wave, small wave, or foam but the ocean water is the same. In the same way, in meditation that space of peace is forever shining but sometimes covered like the clouds can cover the sun. The sun is always shining is it just now always visible. In the same way, the true Self which is forever pure and peaceful always there.
Meditation on your true Self or peace allows you to know yourself as that unchanging peace in all situations.
For more info and Meditation Teacher Training Course Manuals and Knowingness Meditation: Enlightenment is Now, by Shree peace see transformationmeditation.com