Day 247: The Weight of Sin

Sins are rightly evaluated according to their gravity. The distinction between mortal and venial sin, already evident in Scripture, became part of the tradition of the Church. It is corroborated by human experience. CCC 1854

Today's reading from the Catechism is on the weight of sin, or more specifically, how they are classified as mortal and venial. That there are differences in the kinds of sins, and their weight upon the grace given to us by God, is clear from the Scripture referred to above:

If anyone sees his brother committing what is not a mortal sin, he will ask, and God will give him life for those whose sin is not mortal. There is sin which is mortal; I do not say that one is to pray for that. All wrongdoing is sin, but there is sin which is not mortal. (1 Jn 5:16-17)

The Catechism Compendium summarizes what is "evident in Scripture... part of the tradition of the Church... [and] is corroborated by human experience":

Mortal sin

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. (#395)

Venial sin

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. (#396)

The Catechism Companion, Vol III has some good commentary on this, especially on giving in to despair against Holy Spirit:

Mortal sin destroys love in our hearts and takes us out of right relationship with God so we are no longer in a state of grace. Venial sin is wounding. Though it still allows love to exist and does not kill the life of God in our soul, it makes it easier for the Evil One to deliver a killing blow... God wants to forgive all our sins, to heal us and reconcile us to himself. "But the blasphemy against the Spirit will not be forgiven" (quoted in CCC 1864). This is when we choose not to allow God to forgive us and say no to being saved by him. (p. 10)