Ah, if man knew when gloomy death was coming,
he would not sleep thus
but would long for the kingdom of heaven.
(Latin: Ah, homo si sciret quando mors atra veniret,
non sic dormiret, sed caeli regna sitiret.)
The source for the proverb is Philosophia Patrum by Julius Wegeler (GoogleBooks). The poster is made with AutoMotivator. The image is by Tom Blackwell (Flickr).