What is Original Sin, and how does it affect us?
Original Sin is part of the human condition by which we are conceived in a fallen state, i.e., without sanctifying grace. It is our inheritance resulting from the sin of our first parents, Adam and Eve.
God created man and woman in a state of holiness and justice and in complete friendship with him. God also gave them freedom to choose good or evil, warning them that evil brings dire consequences. By choosing to sin, Adam and Eve preferred their own desires over God, distrusting him and ultimately going against their own good. This Original Sin deprived them of the original justice and holiness they had enjoyed. (Cf. CCC 398)
Their transgression had consequences for all humanity—including suffering, death and a loss of God's friendship. Original Sin infects each person at conception, rendering us vulnerable to sin by clouding our judgment and weakening our will. As a result, we are inclined toward disordered appetites, enslaved to our passions, and in need of God's grace to combat evil. The Sacrament of Baptism forgives the guilt associated with our actual sins as well as Original Sin, but our tendency toward sin, or concupiscence, remains.
The only human person exempted by God from this affliction is the Blessed Virgin Mary; Jesus Christ, himself a divine Person, was not conceived according to human generation, i.e., has no biological human father.
-The Didache Bible