According to the ritual marking calculation of 2018 Tamil calendar April 30 will be the Chitra Pournami festival. This special full moon day comes under the ascendency of the star called Chitra. This star is oriented to Chitra-Gupta, a book-keeper of the God of Death, Yama. So the primary reason for anyone to celebrate or follow spiritual rituals on this day is to ask forgiveness for the sins committed purely based on Ignorance and natural sensations.
When a special Pooja of providing sacred food (Prasadham) dedicated to God and then followed by a fire ritual (Dheeparadhanai) will ease out the unknown sins committed in terms of uncontrollable five human sensations and needs.
The act of acknowledging the sins and asking forgiveness on this chitra pournmani day will lead to a positive field of sympathy formed as a result of asking forgiveness to the absolute power of all universes called Bramhmam (The Ultimate Source)
Many historical legends and inscriptions says various stories and phenomenon in carrying out the Chitra Pournami rituals and the specialties of the auspicious occurrence of moon and star.
Meditation on forgiveness and thankfulness towards the Universal Consciousness will react back with compassionate energy as a result of the heart melting understanding of love and affection towards God (The Absolute Source). Meditating on a mantra or to govern a lively action of the universe (Like Breath or Bell Sound) will convert our consciousness into a form of witness for the actions occurring inside our mind.
So we are no more in the guilty conscious space hurting ourselves for the sins we committed once without enough wisdom. These feelings will be converted to outer actions when meditated and so the moral path should be taken in the outer environment for conducting good actions and to love all. This in turn reduces the mental tormenting and stress, so that the blessing will direct the person to do good deeds outside his mental zone and not to commit any further sins in the future.