The seven deadly sins is a concept by a literary author named Chaucer. It is his interpretation of what the seven most deadly sins are. Since it's inception there have been many different takes on it by the church, other authors, and movie producers.
I believe they where created to describe and reflect the obvious sins of the time. Many of these sins are still prevalent in our societies for those who are lusting after something, greedy with their thinking, slothful in their soul, a glutton for punishment, too prideful in there beliefs, envious of anything, or wrathful in there actions, has been bitten.
By what? The things that make us human, for any of these things is natural to have at one point or another. However, these things are needed in moderation, in excess they can be deadly to yourself or others.
How or why the answer is clear answered by faith, the gods did it to us as a consequence for the freedom of choice in our actions.