Mortal sin takes away the merit of the person s previous good actions and deprives one of the right to eternal happiness in heaven. Sincere repentance can reverse these effects. God is not responsible for personal sin because he is all good and all holy, and for everyone who prays, God always provides sufficient grace to overcome temptations. A sin is venial when one of the conditions for a mortal sin is missing. For example, the thought, desire, word, action or omission is wrong but not seriously so, or it is seriously wrong but a person does not clearly see this, or does not fully consent to it.
Venial sin lessens our charity and weakens our practice of the Catholic faith.
It makes us weaker when faced with temptations to serious sin, and hinders our spiritual growth. Although they do not destroy the life of grace, we should avoid venial sins because they are an offense to God and weaken our friendship with him. They also turn our hearts away from God and toward some created good instead, which makes it easier to commit more serious sins. Sins of omission are the failure to do something one should have done. Sins of omission may be mortal or venial depending upon what we have failed to do.