Purusha is a Sanskrit word that in our ordinary lives corresponds to the conscious person. It is in the background of our mind, our feelings and our emotions. It has various levels and aspects depending on the development operating in a being but in general he is the ‘witness’. Everything is reflected in the Purusha. He is this person who looks at himself, talking, being moved, suffering, desiring, enjoying.
For those who practice mindfulness meditation, he is the quiet and observant person developed with the habit of meditating and who also achieves and installs a semblance of peace and mastery of his life. It is as well the ‘special-seeing’ (special :Vi, seeing : Passana) or 'insignt' in the tradition of Buddhist meditation. As a general rule, it is the observer, who, if reinforced, allows us to 'manage' our lives with serenity.
Chaitya Purusha is the form of the conscious being above described but related to the soul, with our Divine spark, it is the true and central being, located within the background as well, in the middle of the chest, no bigger than the thumb, say the Upanishads (Vedanta). When we, during a meditation, focus on this spot, for example by using an image, a light, a candle or other positive things, one can develop in us the essential being and make it come at the foreground of our being, thus becoming a guide in our life, provided perseverance ... a lot of perseverance. At some point or another, perhaps even at the beginning of our general practice of peaceful concentration, we will feel this little pressure in the middle of the chest, it can go along later, and first of all non-permanently, with a confidence, or a feeling of well-being, a joy, a capacity for contemplation, or all of them if a spiritual practice is developed. That is, if an inner intensity develops in this direction.
Chaitya Purusha lies in everybody, but expressed differently and with diverses intensities from one individual to another. In general it influences us throughout our normal life - if there is something such as 'normal' life. Mentally first, infusing a need for honesty in our judgments, our thoughts, emotionally, sentimentally, trying for instance to instill in them a magnanimity of spirit, or by growing affection, love and physically in this need to take care of our body.
It will express itself as the 'heart', full of gratitude in the christian or the muslim. For an agnostic, an atheist, a buddhist, it can be altruism, compassion, being turned to beautiful things, and harmony (which obviously does not mean that the religious people do not possess such qualities, and that the others do not express gratitude, I mention inclinations and characteristics, that one may say are just clichés, I agree but its for the sake of clarity). In its candid and pure form, it is, among babies, this spontaneous joy which one wonders where it comes from when it expresses itself in a cry of joy without anything around the little being seeming to have provoked it . Later, the child, cruel by ignorance, or angry at times, will instinctively have healthy reactions that many adults have lost: they will not be fooled by misbehavior, sensitive to the suffering of the other , naturally happy. I do not mean that adults will have permanently lost these qualities but most of the time the central and true being will be covered by concepts and mental ideas received in their education and upbringings. Or, else, have experienced painful events or sometimes even have been abused, if not mistreated, which will confuse them and veil the true being. And, having personally experienced it, I can say that puberty and adolescence are often these worst moments of perdition. Later, most of us begin to build this true central being - the psychic being, according to Sri Aurobindo - a term that I find difficult to use, because the psychic word defined nowadays elements rather related to the psychology having nothing to do with it - with the help, or not, religious, spiritual, therapeutic, etc. When it 'works' quite consciously it accelerates the process of inner and, by extension, external development of the individual.