An excerpt from St Alphonsus de Liguori's (1696-1787) book entitled "Preparation for Death" published in 1758 at the age of 62
My brother, in this picture of death behold yourself and what you must one day become. "Remember that dust thou art, and unto dust thou shalt return". Consider that in a few years, and perhaps in a few months or days, you will become rottenness and worms. By this thought Job became a saint. I have said to rottenness: Thou art my father: to worms, my mother, and my sister (Job 17:14).
All must end; and if, after death, you lose your soul all will be lost for you. Consider yourself already dead, says St. Laurence Justinian, since you know that you must necessarily die. If you were already dead, what would not desire to have done? Now that you have life, reflect that you will one day be among the dead. St Bonaventure says, that, to guide the vessel safely, the pilot must remain at the helm; and in like manner, to lead a good life, a man should always imagine himself at the hour of death. Says St Bernard, "Look to the sins of your youth, and be covered with shame". "Remember the sins of manhood and weep." Look to the present disorders of your life; tremble, and hasten to apply a remedy.
When St Camillus de Lellis saw the graves of the dead, he said within himself: If these return to life, what would they not do for eternal glory? And what do I do for my soul, who have time? This the saint said through humility. But my brother, you, perhaps, have reasons to fear that your are the fruitless fig-tree of which the Lord said: Behold, for these three years I come seeking fruit on this fig-tree, and I find none" (Luke 13:7) You have been in this world for more than three years; what fruit have you produced? Remember, says St Bernard, that the Lord seeks not only flowers, but fruits; that is not only good desires and resolutions, but also holy works. Learn then to profit of the time which God in His mercy gives you; do not wait until you desire time to do good, when time shall be no more. Do not wait till you are told, Time shall be no longer; depart; the time for leaving this world has arrived; what is done, is done.
At first this might seem all doom and gloom but in reality it is joy. We still have time here on earth to amend our lives! In his "Affections and Prayers" the saint writes "O Jesus my Redeemer! I thank Thee for not having taken me out of life when I was Thy enemy ... Had I died on such a day or such a night, what should be my lot for all eternity?" and later he prays to God to give him just a little time longer to do penance for those past transgressions. God certainly took him up on this offer: St Alphonsus lived to the ripe age of 91, and most of that time suffered from painful arthritis in the neck, so much so he couldn't life his head above his shoulders, his chin constantly on his chest and his beard causing a painful wound there.
When ever I have the misfortune of committing a mortal sin (if it's not one thing, it's another: either missing Sunday Mass or -ahem- other sins), I think about this prayer and cannot wait to get into the Confessional. I also look back on the time before my conversion, especially during my 20's and just marvel that the Lord put up with me for so long. And since, as well. "This is the day which the Lord hath made: let us be glad and rejoice therein." (Psalm 117:24 Douay-Rheims)