Here is the teaching of the Church:
Adam and Eve were created perfect by God and placed by him in a garden – Paradise, if you will. The Church teaches that they were real people. This garden was not heaven, but a paradise where they were protected from harm and had everything they needed. They had all the natural gifts man could have, **plus preternatural gifts given them by God. These preternatural gifts enabled them, unlike us, to have complete control over their wills, intellect and emotions. **Under God’s special protection, they need never have sinned, or become sick or even die, God’s plan being to take them to himself in heaven when their lives were through. Adam was thus the perfect representative of us all, possessing every advantage.
There was a test involved, however, which we all know they failed. In this test they were representing all of mankind as it’s perfect representatives. None of us imperfect men facing this test, left to our own devices, would have stood a chance. It was a test of their free wills, without which no one can truly love anyone else, including God. **As a result of this failure, man lost paradise and all the preternatural gifts (which resulted in what we call “original sin”). **Since that time each man has compounded this failure by personal sin upon sin, thus making him incapable of meriting heaven.
Thanks be to God who, in his mercy, sent us a Saviour, Jesus Christ, who through his sacrifice on the Cross reversed Adam’s failure, paid for our sins and made is possible for us, through faith and baptism, to be restored to fellowship with God.
Baptism takes away all our sin (both Original and, if we are adults, any actual sins commited up to that time) so that we no longer are enslaved to sin. We are given Sanctifying Grace, the Gifts of the Holy Spirit, and the three Theological Virtues. However there remains a type of wound called *concupiscense * (what Protestants call the sin nature) that still *inclines *us to sin. That, plus external temptation, plus our free will is what make it possible for us to sin.
Through faith and our obedience in God’s grace, however, we can strive to resist sin, cultivate virtue, and thus one day be with God in heaven as was his plan all along.
Hope that helps.