Question:
Answer:
Sins of omission are sins that leave undone the good or duties that we are obliged to. They vary in their gravity. For example, if I were to choose not to attend Mass on Sundays or holy days of obligation with full knowledge and deliberate consent, then I would be mortally culpable. If, however, I were to not wash the pile of dishes that my wife can’t get around to washing due to my laziness, then I would be venially culpable. Nevertheless, each of these sins would be sins of omission.
We could also throw in Jesus’ list of the corporal works of mercy in Matthew 25:31-46 as a list of some sins of omission.
Morality doesn’t just consist of avoiding evil but also doing good. Hence St. Thomas Aquinas’s articulation of the first principle of morality: “Good is to be done and pursued, and evil is to be avoided” (Summan Theologiae, I-II:94:2).