The seven deadly sins, often shown in daunting capital letters, are sins defined by the early Catholic Church as mortal or cardinal sins. As such, committing one of them was, and still is to some people, a one-way ticket to eternal damnation, if a person died without the Sacrament of Reconciliation.
These sins are far more significant than other small sins one might commit, called venial sins. It was thought that lesser sins might not bar the way to heaven, if one died without the benefit of having confessed. However, the seven deadly sins were a sure impediment without true repentance and forgiveness. They harmed the soul, and were a significant affront to God.
The seven deadly sins are Pride, Envy, Wrath, Sloth, Greed, Gluttony and Lust. They each came to be associated with a certain demon as well. For example, Pride and Wrath were associated with Satan, Greed with Mammon, and Lust with Asmodeus. Leviathan was associated with Envy, Belphegor with Sloth, and Beelzebub with Gluttony. For many the world of demons was very real, and it was thought demons specifically tempted people to stray from the path of God.
There were also punishments in hell ascribed to each of the sins. First and foremost, according to Dante, is that committing one of the seven deadly sins meant never being able to escape from hell or see the face of God. In fact the agony in this permanent separation from God was the highest punishment.
Later, theologians tried to determine exactly what one would suffer for committing one of the seven deadly sins. Thus, for example, a person who was proud was broken on the wheel, the envious were placed in frozen water, the wrathful were dismembered, and the slothful were thrown into pits full of snakes. The greedy were boiled in oil, and the gluttonous had to eat toads. Those who were lustful, as in practicing adultery or unapproved sexual behaviors would be buried in fire and brimstone.
Each of the seven deadly sins contrasts specifically with the seven virtues. Instead of lust, one should practice chastity. Wrath or anger is opposite to meekness or composure. The greedy should instead be charitable, and humility helps to conquer pride. Sloth or idleness opposes diligence or zeal for work, and gluttony is opposite to temperance. Envy should be stamped out by kindness or admiring other people’s gifts and abilities.