The doctrine of original sin, closely connected with that of redemption by Christ, provides lucid discernment of man’s situation and activity in the world. By our first parents’ sin, the devil has acquired a certain domination over man, even though man remains free. Original sin entails “captivity under the power of him who thenceforth had the power of death, that is, the devil”. Ignorance of the fact that man has a wounded nature inclined to evil gives rise to serious errors in the areas of education, politics, social action and morals.
The consequences of original sin and of all men’s personal sins put the world as a whole in the sinful condition aptly described in St. John’s expression, “the sin of the world”. This expression can also refer to the negative influence exerted on people by communal situations and social structures that are the fruit of men’s sins.
This dramatic situation of “the whole world [which] is in the power of the evil one” makes man’s life a battle:
The whole of man’s history has been the story of dour combat with the powers of evil, stretching, so our Lord tells us, from the very dawn of history until the last day. Finding himself in the midst of the battlefield man has to struggle to do what is right, and it is at great cost to himself, and aided by God’s grace, that he succeeds in achieving his own inner integrity.
From the Catechism of the Catholic Church 407-409