"Through one man sin entered the world, and through sin, death, and thus death came to all, inasmuch as all sinned." (Romans 5:12)
Original sin can be understood as the sin of Adam originally committed in the garden, or as the privation of grace which is inherited by all men. As the sin in the garden, it was specifically Adam's sin (not Eve's) that caused the Fall of the human race - since all men (including Eve) come from Adam. As the privation of grace, original sin is transmitted to all by generation not merely imitation.
Adam spoke for us all when he sinned and, although each of us did not personally choose to sin, original sin is considered "voluntary" insofar as is the effect of the voluntary choice of Adam. However, even as in Adam all sinned, so also in Christ we have been victorious over sin and death! Just as Adam spoke for all when he disobeyed, Christ Jesus has spoken for all who are baptized into him and in Christ we have been obedient!
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