What is the biblical understanding of Original Sin? Another way of putting that question would be to ask, How did we all become sinners in the first place?
In Adam’s fall sinned we all.
James Boice writes,
That all people sin might be affirmed by any honest secular writer. What a secular writer is not likely to say, however, but which the Bible says plainly, is that there is a necessary connection between all individual occurrences of sin. In other words, the point is not merely that all people sin and are therefore sinners, though that is true. The point is that all sin because they are sinners. The original sin of Adam and the guilt of sin in some inevitable way passed upon the entire human race. The biblical view is that God holds the entire race to be guilty because of Adam’s transgression. (Foundations of the Christian Faith, p.205)
So while many might be willing to acknowledge the fact that all people sin and are sinners, few and far between are those people who are also willing to acknowledge how we all ended up that way.
In Adam’s fall sinned we all.
The Westminster Shorter Catechism affirms this biblical teaching as well:
Q.16. Did all of mankind fall in Adam’s first transgression? A. The covenant [of works] being made with Adam, not only for himself, but for his posterity; all mankind, descending from him by ordinary generation, sinned in him, and fell with him, in his first transgression.
Similarly, The Heidelberg Catechism affirms Original Sin:
Q.7. Then where does man’s corrupt nature come from? A. From the fall and disobedience of our first parents, Adam and Eve, in Paradise. This fall has so poisoned our nature that we are born sinners – corrupt from conception on.
So Adam was not only the first sinner, but also the first representative (federal head) of the entire human race. So when he sinned and fell, he did so not only for himself, but on our behalf as well. And the proof is in the result – we are all sinners. We all sinned in Adam; we all fell in Adam, just as if we had ourselves partaken of the forbidden fruit.
Thankfully, by God’s grace that is not the end of the story. The Lord Jesus Christ came into the world as the “last Adam” (1 Corinthians 15:45), as a new federal head or representative, not unto sin and death, but unto righteousness and life! The Apostle Paul writes,
Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. 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. Now the law came in to increase the trespass, but where sin increased, grace abounded all the more, so that, as sin reigned in death, grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord. (Romans 5:18-21 ESV)
Sin abounded in Adam, but grace abounded all the more in Jesus Christ! His death on our behalf brings us justification & life through faith in Him.
In Adam’s fall sinned we all, but in Jesus Christ we have the perfect righteousness of the incarnate Son of God Himself! No wonder Paul says that grace abounds!