Thomas Aquinas doctrine on Sin

According to Thomas Aquinas in his philosophical work Summa Theologica, sin is defined as "the turning away from the immutable good" by breaking the moral standards set by God. His definition of sin was highly influenced by St. Augustine, who viewed sins as actions that deliberately went against God. While Aquinas believed that all sins were severe, he felt that the severity of the sin depended on how much the damaged one's relationship with God. Because of this, an action only qualified as a sin if they were committed deliberately and with full knowledge that the action is against God's will.
Thomas Aquinas was also one of the earliest theologians to define the difference between a mortal and venial sin. A venial sin, as defined by Aquinas, describes a minor sin that, while requiring repentance, does not separate oneself from God or result in eternal damnation. A mortal sin, however, is more grave and results in immediate damnation if one does not renounce the sin before death. As Aquinas defined them, however, even venial sins could become mortal sins if they became an addiction or obsession.
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