"Watch; for ye know not, what hour   your Lord doth come. If only this were remembered,   there would be no sinners. But it is not remembered,   although everyone knows that it is unquestionably true.   Even the strictest ascetics were not strong enough to   easily keep this in mind, and made efforts to fix it in   their consciousness so that it would not leave—one   kept a coffin in his cell, another begged his co-ascetics   to ask about his coffin and grave, another kept pictures   of death and judgment, another in other ways. If death   does not touch a soul, the soul does not remember it. But   in no way can what immediately follows death not touch a   soul; a soul cannot but be concerned about this, since it   is the judgment of its fate for eternal ages. Why does a   soul not remember this? It deceives itself that death will   come not soon, and that perhaps somehow things won’t   go badly for us. How bitter! It goes without saying that a   soul which abides in such thoughts is careless and   self-indulgent. So, how can it think that judgment will go   favorably for it? No, one must behave like a student who   is facing an exam: no matter what he does, the exam does   not leave his head; such remembrance does not allow him to   waste even a minute in vain, and he uses all his time to   prepare for the exam. When will we acquire a mindset like   this!"
- Saint Theophan the Recluse 
Reference: http://days.pravoslavie.ru/en/Days/20110813.htm