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Engaging Faith: Practical lesson ideas and activities for Catholic Educators

April 18, 2016

Considering Serious Sin

Review with your students the definition and conditions of mortal sin, perhaps in anticipation for celebrating the Sacrament of Penance.


A mortal sin is a serious violation of God’s law of love that results in the loss of God’s life (sanctifying grace) in the soul of the sinner.

Conditions of Mortal Sin

  1. The moral object must be of grave or serious matter. Grave matter is specified in the Ten Commandments (e.g., do not kill, do not commit adultery, do not steal, etc.)
  2. The person must have full knowledge of the gravity of the sinful action.
  3. The person must completely consent to the action. It must be a personal choice.

An additional and maybe obvious condition for mortal sins is that the action must be completed.


Print out a sheet with the following twenty items. Have the students mark an “S” by each action they believe involves serious or grave matter and may lead to the occasion of mortal sin.

  • Dating someone behind the back of a boyfriend or girlfriend
  • Killing an enemy soldier in war
  • Teasing a classmate
  • Lying to a parent about your whereabouts
  • Having an abortion
  • Assisting the suicide of a terminally ill patient
  • Using illegal drugs
  • Getting drunk
  • Smoking cigarettes
  • Having premarital sex with a person you love
  • Having sex as a one-time hook-up
  • Masturbating
  • Telling a friend’s secret
  • Spreading rumors about a classmate
  • Cheating on a test
  • Cheating on the SAT
  • Shoplifting a candy bar
  • Shoplifting a jacket
  • Sneaking into a movie theatre without paying
  • Tagging or graffiti-ing private property


Conduct a follow-up classroom discussion using the following prompts.

  • Which action do you feel is most grave or serious? Why?
  • For any action you marked as serious, explain how each of the three conditions for a mortal sin must be involved to make it a mortal sin.
  • Choose one action you did not mark. Tell why you do not consider it to be serious.
  • Share a definition of sin in your own words.

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