In order to find out the root cause of sins, first let's see what is a sin? Our ancient philosophy defined sins as of two types - Paapam and Paathakam. One commits a Paapam when he doesn't properly discharge his prescribed daily duties. These duties include the daily worship, being kind to all the living beings, special worships on the festival days, meditation, contemplation etc. And one commits Paathakam when he performs any prohibited acts such as, stealing other's possessions, murder, adultery, etc. These two are commonly known in English as omission and commission mistakes.
Now let's see why most of us commit these mistakes, and why the Mahatmas, or enlightened souls, don't commit these sins. When it comes to omitting our prescribed duties, the most frequent excuse we give is lack of time or some kind of illness or discomfort of the body. But when you look at the lives of the mahatmas, they never miss their duties no matter how sick they are, or how busy they are. So what is the thing that is holding us back from performing our duties, which is not affecting the mahatmas? If you think deeper, it's the "identification of ourselves with our bodies." Because we think we are the physical body, we give higher importance to its illness and discomfort. Also, most of our day goes in nurturing the body and all other bodies related to it viz. our family members, relatives, friends and coworkers. That's the reason we say we are too busy to perform our prescribed spiritual duties. But when it comes to mahatmas, they don't identify themselves with their bodies. They instead experience their true existence as the soul, or Aatma. Thus, they always perform their spiritual duties irrespective of whether they are busy with their worldly duties or seriously ill.
And coming to the commission mistakes, or Paathakams, it's again the "identifying oneself with the body," which is the root cause. people do the prohibited acts like stealing and killing because they identify themselves with the body and will do anything to protect and nurture it. And any thing or person outside of that body is "the other" and their feelings/difficulties/joys are not ours! But the mahatmas, as they identify themselves with the all-pervading soul, see everything else in this universe as themselves and feel their pains and joys, and thus never even think of hurting any other living or non-living being. There is no "other" for them as the whole universe is "self".
Every spiritual seeker agrees that identifying oneself with their body is a weakness and tries to overcome it, but when you tell them that it's the root cause of all sins, they may not agree. But now we know from the above analysis that it's the root cause of all sins and thus needs to be overcome as soon as possible. While we enlighten ourselves to identifying with the soul, there is a simple remedy prescribed to overcome the consequences of the sins we already committed because of this ignorance.
Yatkrutyam Tannakrutam, Yadakrutyam Krutyavat Tadaacharitam,
Ubhayoh Praayaschittam Shiva Tava Naamaakshara Dvayochcharitam. Shiva Shiveti Shiveti Shietimat, Bhava Bhaveti Bhaveti Bhavetimat, Hara Hareti Hareti Haretimat, Bhaja Namasshivameva Nirantaram.
"I ignore my prescribed duties and also commit the prohibited acts as if they were my ultimate duties. Oh Lord Shiva! the penance for both these sins is the continuous recitation of the two syllable words that represent your names like Shiva, Bhava, Hara, etc."
Our Gurudev, Sri Babuji Maharaj, used to tell that identifying oneself with the body is like a tenant claiming ownership of his rented house. In physical world, when a tenant claims ownership of the house, he will be immediately evicted from the house forcefully. But in the spiritual world claiming ownership of this rented house, which is our body, seems to extend the tenancy! As long as one doesn't overcome this ignorance and enlighten oneself to the identification with the soul, he will be forced to get reborn into multiple rented bodies and continue to suffer the vicious cycle of rebirth. That's why they say "Paapi chirayu", a sinner gets the longest life.
