Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned— for sin indeed was in the world before the law was given, but sin is not counted where there is no law.  Yet death reigned from Adam to Moses, even over those whose sinning was not like the transgression of Adam, who was a type of the one who was to come.
 But the free gift is not like the trespass. For if many died through one man’s trespass, much more have the grace of God and the free gift by the grace of that one man Jesus Christ abounded for many.
Just as sure as you know that there is evil in the world and that it has made it’s way even to you, you can have confidence that the sacrifice and salvation of Christ can make it to you too.
That is what Paul is explaining here. Just as sin came into the world through one man, who you never met and you never saw, so also salvation came into the world through one man that you never met and never saw. The work of Adam permeates through all of human history and human experience. The temptation, the sympathy of struggle with his friend(s) and the fall all sum up the same sorts of temptations and failures that we all experience every single day.
If that experience of Adam’s can affect us thousands of years later, we can also be confident that the experience of Christ — the second Adam — can affect us today too. Death and sin spread all over the place to every corner of the world. Today, salvation and the good news of forgiveness spreads all over the world. People are being freed from the law of sin and death every day as they come to faith in the saving work of Jesus Christ.
The free gift of Christ is received by faith in His life and work. The grace of God was His own purchase of our lives by Jesus’ death on the cross. That sacrifice didn’t blot out just one single sin for one person, but all sin for all who call on His name. One sin of Adam’s resulted in zillions and zillions of sins by mankind. One sacrifice by Jesus wipes out zillions and zillions of sins that each one of us will ever commit.
We don’t have to be afraid of sinning and we don’t have to be afraid that maybe Christ didn’t die for enough. Our lives are covered in His grace. We no longer have to live out of fear. We can live freely out of love and celebration, which is a fuller life anyway.