(Book: First Apology, by Justin Martyr, courtesy of The Christian Classics Ethereal Library.)
At the end of Chapter 17, Justin warned Caesar that someday he was going to be judged by a Christian God and possibly punished for his conduct as Caesar. Having made that thinly veiled threat, he begins Chapter 18 by inviting Caesar to consider those kings who have already died.
For reflect upon the end of each of the preceding kings, how they died the death common to all, which, if it issued in insensibility, would be a godsend to all the wicked.
Justin’s first proof of life after death is an appeal to the fallacy of the consequences. We don’t want the wicked to escape unpunished, therefore they must continue to live on after they die so that God will be able to punish them, Q. E. D. Believe it or not, his argument actually gets worse from there.