Sin

Any thought, speech, or action that is contrary to the love of God and neighbor is a sin.

Sin harms man’s relationship with God and can prevent him from attaining eternal life with God in Heaven.

Original Sin is inherited from Adam and Eve while actual sins are committed by the individual.

Sins of commission are doing things that are forbidden by God. Neglecting to do things that are commanded by God are sins of omission.

Mortal sins are serious sins that deprive man of sanctifying grace and separates him from God. For something to be considered a mortal sin it must invole a serious matter, man must know that it is a sin, and he must do it on purpose.

Less serious sins are referred to as venial. Venial sins weaken the ability to resist mortal sins.

All sin indicates an unhealthy attachment to material things instead of God and requires repentance, confession, and penance.

Misusing the powers given by God:

Not an accident, a mistake, or simply breaking a rule:

So for one who knows the right thing to do and does not do it, it is a sin.
James 4: 17

Criteria determine what is a sin:

Missing the mark:

Sin is an offense against reason, truth, and right conscience; it is failure in genuine love for God and neighbor caused by a perverse attachment to certain goods. It wounds the nature of man and injures human solidarity. It has been defined as “an utterance, a deed, or a desire contrary to the eternal law.”
Catechism of the Catholic Church 1849

Some sins are worse than others:

Sins can be mortal or venial:

Sin can occur by thought, word, action, or inaction:

It is possible to see leprosy as a symbol of sin, which is the true impurity of heart that can distance us from God. It is not in fact the physical disease of leprosy that separates us from God as the ancient norms supposed but sin, spiritual and moral evil. This is why the Psalmist exclaims: “Blessed is he whose fault is taken away, / whose sin is covered”, and then says, addressing God: “I acknowledged my sin to you, / my guilt I covered not. / I said, “I confess my faults to the Lord’ / and you took away the guilt of my sin”. The sins that we commit distance us from God and, if we do not humbly confess them, trusting in divine mercy, they will finally bring about the death of the soul.
Pope Benedict XVI, Angelus Address, February 15, 2009

God forgives sin: