"He who through his mind, speech and action does work that is against his varnashrama dharma (duites as per his caste) falls into hell."

"varṇāśramaviruddhaṃ ca karma kurvanti ye narāḥ, karmaṇā manasā bācā nirayeṣu patantite " ~ Vishnu Purana. 
"He who through his mind, speech and action does work that is against his varnashrama dharma (duites as per his caste) falls into hell." 
Sins, there are many kinds. There are so many kinds mentioned in our scriptures that categorising them would be difficult. Generally, a sin is committed when the prescribed laws of the sages are violated either by mind, body or speech. So there are these main three kinds of sins, Sins committed by the body , the mind and by speech. Sins committed by body are - appropriation of un-offered wealth, slaughter without sanction and adultery.
Sins committed by speech are harsh speech, telling a lie, backbiting and idle or irrelevant talk.
Sins committed by mind are thought of injuring another by thought or deed and identification of the self with the body.
To remove these sins and purify our heart 'Tapas is advised at three levels- at the level of the body, the mind and at level of speech.‪ By the practice of penance at these three levels- the mind, the senses and the body are , as if, put on fire and "heated". Just as the impurities of gold are burnt out when it is heated by fire and the purest ore is thus obtained, even so the impurities of man are removed by performing this 'Tapas'.
By worship of God, and in observance of straightforwardness, continence and harmlessness, the sins committed by the body are removed.
By speaking speech that is beneficial, truthful and agreeable- as well as with the wholesome study of the Vedas and practice of Japa, the sins committed by speech are removed. For such a person would never lie, backbite or speak harsh speech or indulge in idle talk.
By maintaining cheerfulness of the mind, having a habit of constant meditation on God, and having control of mind ; the sins committed by the mind are eradicated. For such a person slowly weakens his identification with the body.
The penance or tapas at all these levels- can be Sattviks, Rajasika or Tamasika.
A Sattvika Tapas is done without any desire for a reward with full faith in God.
A Rajasika Tapas is performed to secure respect, for object of showing to others- and its result is transient.
A Tamasika Tapas is done through perversity with torture to the body, mind with the object of causing injury to another.
Both Sattvika and Rajasika Tapas no doubt will save a man from the commission of new sins, so long he is engaged in its practice.
Hari Om Tat Sat Namah Shivaya!!