This excerpt is taken from pages 124,125 of Dr. Norman Geisler’s Systematic Theology Volume 3:
The Effects Of Sin On Adam’s Descendents
Adam’s sin affected not only himself but also all of his offspring – all of us have sinned “through one man” (Rom. 5:12). All of Adam’s descendents were present in himpotentially, seminally, and/or legally (judicially), since as the head of the race he was our legal representative (Rom. 5:18-21).
The Judicial (Legal) Effects of Adam’s Sin
As our legal representative, Adam sinned on our behalf, and we received the legal consequences of his choice. In other words, Adam had the God-given power of attorney for the whole human race, and when he exercised it for ill, the consequences of his sin were directly imputed to all of his posterity – which is all of us. Paul says,
Therefore, as through one man’s offense [Adam’s sin] judgment came to all men, resulting in condemnation, even so through one Man’s righteous act [Christ’s death] the free gift came to all men, resulting in justification of life. For as by one man’s [Adam’s] disobedience many were made sinners, so also by one Man’s [Jesus’] obedience many will be made righteous. (Rom. 5:18-19)
As legally or judicially, then, the consequences of Adam’s sin were imputed to all his natural offspring, we will later learn that Christ, “the last Adam” (1 Cor. 15:45), revoked what Adam did, making every human being legally and potentially savable.
Hence, all of us stand guilty before God because of what Adam did on our behalf; his sin on behalf of the race was imputed to the race. Clearly, the all (or many) were not made sinnersactually, since they did not actually exist at that time. However, they werepotentially and legallypresent in Adam, and, as such, received the imputation of the consequences of his sin.
But we are still left with the questions, “Why did God give Adam a power of attorney for the whole human race?” and “How can that be just, when we never voted Adam into that position, or gave our consent to it?” Here I refer you to my comments about unanswered questions in the introduction to this series. We get the point, we understand the general idea the Bible is conveying, but there are enough unanswered questions to preserve free will, to allow someone who wants to reject God to convince themselves that they’re right.