Compendium issued by Pope Benedict XVI
- When does one commit a mortal sin?
1855-1861
1874
One commits a mortal sin when there are simultaneously present: grave matter, full knowledge, and deliberate consent. This sin destroys charity in us, deprives us of sanctifying grace, and, if unrepented, leads us to the eternal death of hell. It can be forgiven in the ordinary way by means of the sacraments of Baptism and of Penance or Reconciliation.
- When does one commit a venial sin?
1862-1864
1875
One commits a venial sin, which is essentially different from a mortal sin, when the matter involved is less serious or, even if it is grave, when full knowledge or complete consent are absent. Venial sin does not break the covenant with God but it weakens charity and manifests a disordered affection for created goods. It impedes the progress of a soul in the exercise of the virtues and in the practice of moral good. It merits temporal punishment which purifies.
Catechism:
863 Venial sin weakens charity; it manifests a disordered affection for created goods; it impedes the soul’s progress in the exercise of the virtues and the practice of the moral good; it merits temporal punishment. Deliberate and unrepented venial sin disposes us little by little to commit mortal sin. However venial sin does not set us in direct opposition to the will and friendship of God; it does not break the covenant with God. With God’s grace it is humanly reparable. "Venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity, and consequently eternal happiness."134
While he is in the flesh, man cannot help but have at least some light sins. But do not despise these sins which we call “light”: if you take them for light when you weigh them, tremble when you count them. A number of light objects makes a great mass; a number of drops fills a river; a number of grains makes a heap. What then is our hope? Above all, confession.135
You may be thinking of that underlined line…where we can be “disposed” to mortal sin…
Also you may be thinking of say what ordinarily would look to be venial matter…can be grave…such as taking a small amount of money from a starving man…that sort of thing.