The Doctrine of Original Sin is the idea that all humanity after Adam has been born sinners because of Adam’s sin. Whether this doctrine is true or not is irrelevant to the truth of Christianity . . . because one can still be an orthodox Christian without holding strictly to it. I say strictly because I think there are two variations of original sin that need to be identified here.
The first variation is a form of imputation. This is the idea that because Adam sinned, his guilt has been imputed to all humanity, thus all humanity is guilty of Adam’s sin. Not only is this weakly supported in Scripture, it’s not universally held among all Christians, either . . . understandably so. However, in defense of this idea, we have seen times in our justice system where this sort of thing has easily occurred. For example, if an employee were to commit a crime, the employer might be held responsible for that same crime, even though the employer didn’t commit that crime, personally.
Another defense of imputation might be to call on God’s omniscience. If God knows everything, He obviously knows what we would have done if we were put in Adam’s place. Even though I’m not omniscient, I feel quite confident in saying that all humanity would have acted the same way Adam did, given similar circumstances. If that’s the case, one could argue that we were rightly represented by Adam as our proxy.
Nonetheless, imputation remains controversial, which is why I remain open-minded to it. A more modest variation of original sin might be more widely accepted, which takes me to my next point.
Corruption is the other variation. The idea here is that because Adam sinned, all of his offspring have inherited a sort of corruption. In other words, we have basically inherited our sinful nature and are prone to sin, which is why, in fact, we do.
Whether you agree with this doctrine or not, one thing can be certain for the believer: Regardless of original sin, all have sinned and fall short of the glory of God (Romans 3:23), and the wages of sin is death (Romans 6:23). However, thanks be to God who gives us the victory through our Lord Jesus Christ (1 Corinthians 15:57).