Pope Gregory the Great (604AD) described the seven deadly sins as:
Pride, Envy, Anger, Avarice, Sloth, Gluttony, Lust
Why were they called ‘Deadly’? The church made a division between sins which were venial and could be forgiven without the need for the sacrament of Confession and those which were capital and merited damnation. Capital or deadly sins were so called because they could have a fatal effect on an individual’s spiritual health.
You might imagine that the church would want to prevent people even thinking about such spiritually dangerous actions. But there were two good reasons why the church felt it was important to educate people:
so that they would not commit these sins without realising how serious they were,
so that they would be able to confess any such sins and gain absolution.
This desire to educate the laity about the seven deadly sins can be particularly associated with the Fourth Lateran Council (1214). This Council established the practice of annual confession for all, declaring that:
All the Faithful of both sexes shall, after they have reached the age of discretion, faithfully confess all their sins at least once a year to their own (parish) priest and perform to the best of their ability the penance imposed, receiving reverently at least at Easter the sacrament of the Eucharist, unless perchance at the advice of their priest they may for a good reason abstain for a time from its reception; otherwise they shall be cut off from the Church during life and deprived of Christian burial in death. Wherefore, let this salutary decree be published frequently in the churches, that no one may find in the plea of ignorance a shadow of excuse.
For this programme to be carried out, priests had to be educated to counsel the penitents and the laity had to be able to recognise and recall their sins. To address this need, the church set out syllabuses of material which they required their clergy to learn and to teach to their congregations. Further information can be found in the Catechism of the Catholic Church.