We are not sinners because we sin; we sin because we are sinners.
Like Humpty Dumpty, we all had a great fall, but not by accident, but by deliberate choice. The human race had a Federal Head in the Garden of Eden, namely Adam, who represented the entire human race. When he sinned, he sinned "for us" - we all sinned in him - he acted on our behalf. Because he was our Federal Head, this had huge and drastic consequences for us. Romans 5:12 "Therefore, just as sin came into the world through one man (Adam), and death through sin, and so death spread to all men because all sinned..."
Did you catch that?
We all sinned in Adam. When he disobeyed, he was disobeying on our behalf. His act brought death to us. We died in him. Just as Adam was cut off from the life of God (spiritually) as a result of his sin, all those born after him were born spiritually "dead on arrival" on planet earth. The Bible teaches us clearly that there are two Federal Heads for the human race, Adam and Christ. "As in Adam all die, so in Christ shall all be made alive." (1 Cor 15:22). If we remain only represented by Adam, there is no hope for us whatsoever. Adam failed us all. He offers no redemption. God takes the sin of Adam and imputes it to all the human race. When Adam sinned, we sinned in him. That is the bad news - we were born sinners.
Before we say it is not fair that we are credited with Adam's sin when we were not there in the garden, thousands of miles away, thousands of years ago, we need to remember, that the other side of the coin in imputation (crediting) is that Christ's righteousness is credited to all those who place their trust in Him.
This is the really good news! Let me explain.
Jesus the second Man succeeded where Adam, the first man failed. All that Jesus did, He did for us. He already was perfect and already had a perfect fellowship with His Father. He did not need to come to earth for any reason, except for love. He came here for us. He came here on a mission to save His people from their sin (Matt 1:21) and His mission was accomplished. He could cry out on the cross, "It is finished!" (It is paid for, the debt is removed completely). Because of His work for us, if we will make the Lord Jesus Christ our Lord, we gain all that He accomplished by His perfect life of obedience, His death as our Substitute who died in our place and triumphant resurrection.
Now these words in Romans 5 begin to make sense: 17 "For if, because of one man's trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ. 18 Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. 19 For as by the one man's disobedience the many were made sinners, so by the one man's obedience the many will be made righteous."
Christ took the punishment our sins deserved and God imputed (credits, counts to us) the righteousness of One who obeyed God fully - a perfect righteousness that can never be added to or improved upon.
"Now to the one who works, his wages are not counted as a gift but as his due. And to the one who does not work but believes in him who justifies the ungodly, his faith is counted as righteousness, just as David also speaks of the blessing of the one to whom God counts righteousness apart from works:" - Romans 4:4-6
"For our sake he (God) made him (Christ) to be sin who knew no sin, so that in him (in Christ) we might become the righteousness of God." 2 Cor 5:21
Concerning this concept of the imputation of Christ's righteousness to the believer, Dr. J. I. Packer once wrote, “[God] reckons righteousness to them, not because he accounts them to have kept his law personally (which would be a false judgment), but because he accounts them to be united to one who kept it representatively (and that is a true judgment)."
Have you transferred your trust from your own works or actions and given yourself over to God's mercy found in the only One who can save you, Jesus Christ? If you have, all that Christ is and all He achieved is yours, now and forever. This, ladies and gentlemen, is the gospel (good news) of Christ.
Christ came into the world to save sinners, and He does so when we turn from all self effort or trust in ourselves and instead rely solely on the finished work of the perfect Savior. In Christ there is endless hope; in Adam there's just a hopeless end.
So let me ask you - who represents you, Adam or Christ?
I know that many people struggle with this concept of Adam as our representative, but there's no doubt as to its biblical reality - so perhaps it may be of help to suggest the following as an illustration of the situation. I hope it helps. Here goes:
Imagine for a moment you and I lived in a country (lets make up a name.. the country of Tangeria)... and in that country there was a presidential race and you and I picked a particular candidate (we gave him our vote).
This man was elected president and went to the Tangeria equivalent of the White House to represent us. Once in office he made atrocious decisions even to the point of declaring war on (lets think of a country we know)... Italy ... for seemingly no reason at all.
I fully realize that this illustration would not work in the USA because there are restrictions and limitations about what a President can do (thank God) - there are safeguards in place to prevent this sort of thing from happening, but this is "Tangeria" where no such safeguards are in place, but remember, this is just an illustration.
Now, back to the analogy - IF such a thing happened, you and I would be responsible for the decisions he made because of our vote for him in the election - we put him there by our vote. We gave him the power to represent us as President of Tangeria.
Now lets use this illustration and take that concept over to the book of Genesis and we can see that similarly with Adam, when he did what he did (sinned), he did so as your and my representative. The difference is, of course, that we were not alive back then to vote Adam into office, and that is where I think most people have an issue. However, we should remember this. We (the human race) could not have had a better representative than Adam. Though untested, he was created perfect. He had no track record of sin. The difference then is that rather than WE voting for Adam to represent us, God picked Adam to represent us, and yet, God could not have picked a better candidate for us.
As our representative, when Adam sinned in the garden, we (the human race) all sinned in him. When he wanted independence from God and chose to disobey God, we also wanted the same thing. We are responsible for his actions because all that Adam did, he did on our behalf.