Death is Penal
Death is neither the merely natural outworking of sin nor the cumulative effect of sinning. It is not only sin’s own reflexive “reward” or pay-off. As the “wages of sin” (Rom. 6:23), death is not merely pecuniary but penal. Death is God’s response to sin, a response that is judicial in nature. Death, as his ultimate curse on sin, is his just punishment of sin. Death for Paul, it does not overstate, is inalienably penal. Romans 5:16-18 is decisive on this point.
Richard Gaffin, By Faith, Not by Sight: Paul and the Order of Salvation (Paternoster, 2006), 85-86.