I ran across Romans 5:19 today, and I think it may be one of the clearest verses for understanding the doctrine of original sin.
Romans 5:19—”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.”
The context is that Paul is contrasting Adam’s disobedience, along with the condemnation and death that resulted, with Christ’s obedience, along with the justification and life that resulted. But this verse says something even more specific. The word translated “so” in the ESV is two words in the Greek: οὕτως καὶ. The latter simply means “and,” and the former means “in the same way.” So a more literal rendering could be:
“For as by the one man’s disobedience the many were made sinners, IN THE SAME WAY by the one man’s obedience the many will be made righteous.”
The point is that the means by which we are made sinners by Adam is the same as the means by which we are made righteous by Christ.
So does this teach original sin? One could propose that the way Adam makes us sinners is by his bad example that we follow. If that was the case, then Romans 5:19 would say that Christ makes us righteous in the same way: by giving us a good example to follow. And this is more or less what Pelagians have taught. But Romans is absolutely clear that the means by which Christ makes us righteous is not his good example, in many places, but particularly in 4:3-5:
Romans 4:3-5—”what does the Scripture say? Abraham believed God, and it was credited to him as righteousness. 4 Now to the one who works, his wage is not credited as a favor, but as what is due. 5 But to the one who does not work, but believes in Him who justifies the ungodly, his faith is credited as righteousness”
Righteousness is not first produced in believers. First, it is credited/accounted/imputed to them. They don’t have it inherently to themselves, but it is credited to their account.
So if Romans 4:3-5 teaches that Christ makes believers righteous by crediting them righteousness, and Romans 5:19 teaches that Christ makes righteous the same way Adam makes sinner, then Adam must also credit people sin. The means by which Adam makes people sinners is by crediting them the sin that they don’t yet have, but that he has.
What if someone objects that they don’t accept that Romans 4:3-5 teaches imputation, and that they still insist on taking the verse to mean that Adam makes sinners only by example? If that was the case, then by Romans 5:19 Christ would make people righteous only insofar as being a good example for them. But is that enough? God is a holy God, and he cannot accept sinners. Even if we reject Adam’s imputation of sin to us, we have all sinned ourselves, and stand guilty before God for it. And even if a person was to turn from their sin and live sinlessly for the rest of their life, they would still be guilty of the sins in their past. The only hope for sinners is that Christ would be able to impute his righteousness to us: but the person who rejects imputation in order to avoid original sin can’t then have Christ’s imputation of righteousness.
So, for sinners to have any hope, we need the doctrine of imputation, by which we’re rescued from both our original sin and our own sinful acts by the imputation of Christ’s righteousness.