Mercy without justice makes a mockery of the sacrifice of the Lamb of God. Punitive dealings provide a necessary atonement and restore the moral balance that has been disturbed by sin. Purification, one of the most central of biblical themes, reveals to us both the temporal and eternal perspectives on mankind. Which leads me to a second observation. The death penalty ultimately confronts us with the issue of moral accountability in the present life.
Contemporary society seems totally unwilling to assign moral responsibility to anyone.
Everything imaginable is due to a dysfunctional family or to having had our knuckles rapped while we were in grade-school. Non-Christians and Christians alike are not absolved from the consequences of their behavior. Whether or not faith is professed, penalties for everything from speeding to strangulation apply to all. I come to this view with something of a heavy heart, as some of the most blessed brothers I've known in my Christian walk were on death row. I think of Richard Moore in particular and, of course, Rusty Woomer, about whom I've written in The Body.