From Book II, Ch. 23, of Imitation of Christ, by Thomas à Kempis.
Very soon your life here will end; consider, then, what may be in store for you elsewhere. Today we live; tomorrow we die and are quickly forgotten. Oh, the dullness and hardness of a heart which looks only to the present instead of preparing for that which is to come!
Therefore, in every deed and every thought, act as though you were to die this very day. If you had a good conscience you would not fear death very much. It is better to avoid sin than to fear death. If you are not prepared today, how will you be prepared tomorrow? Tomorrow is an uncertain day; how do you know you will have a tomorrow?
What good is it to live a long life when we amend that life so little? Indeed, a long life does not always benefit us, but on the contrary, frequently adds to our guilt. Would that in this world we had lived well throughout one single day. Many count up the years they have spent in religion but find their lives made little holier. If it is so terrifying to die, it is nevertheless possible that to live longer is more dangerous. Blessed is he who keeps the moment of death ever before his eyes and prepares for it every day.
If you have ever seen a man die, remember that you, too, must go the same way. In the morning consider that you may not live till evening, and when evening comes do not dare to promise yourself the dawn. Be always ready, therefore, and so live that death will never take you unprepared. Many die suddenly and unexpectedly, for in the unexpected hour the Son of God will come. When that last moment arrives you will begin to have a quite different opinion of the life that is now entirely past and you will regret very much that you were so careless and remiss.
How happy and prudent is he who tries now in life to be what he wants to be found in death. Perfect contempt of the world, a lively desire to advance in virtue, a love for discipline, the works of penance, readiness to obey, self-denial, and the endurance of every hardship for the love of Christ, these will give a man great expectations of a happy death.
You can do many good works when in good health; what can you do when you are ill? Few are made better by sickness. Likewise they who undertake many pilgrimages seldom become holy.
Do not put your trust in friends and relatives, and do not put off the care of your soul till later, for men will forget you more quickly than you think. It is better to provide now, in time, and send some good account ahead of you than to rely on the help of others. If you do not care for your own welfare now, who will care when you are gone?
The present is very precious; these are the days of salvation; now is the acceptable time. How sad that you do not spend the time in which you might purchase everlasting life in a better way. The time will come when you will want just one day, just one hour in which to make amends, and do you know whether you will obtain it?
See, then, dearly beloved, the great danger from which you can free yourself and the great fear from which you can be saved, if only you will always be wary and mindful of death. Try to live now in such a manner that at the moment of death you may be glad rather than fearful. Learn to die to the world now, that then you may begin to live with Christ. Learn to spurn all things now, that then you may freely go to Him. Chastise your body in penance now, that then you may have the confidence born of certainty.
Ah, foolish man, why do you plan to live long when you are not sure of living even a day? How many have been deceived and suddenly snatched away! How often have you heard of persons being killed by drownings, by fatal falls from high places, of persons dying at meals, at play, in fires, by the sword, in pestilence, or at the hands of robbers! Death is the end of everyone and the life of man quickly passes away like a shadow.
Who will remember you when you are dead? Who will pray for you? Do now, beloved, what you can, because you do not know when you will die, nor what your fate will be after death. Gather for yourself the riches of immortality while you have time. Think of nothing but your salvation. Care only for the things of God. Make friends for yourself now by honoring the saints of God, by imitating their actions, so that when you depart this life they may receive you into everlasting dwellings.
Keep yourself as a stranger here on earth, a pilgrim whom its affairs do not concern at all. Keep your heart free and raise it up to God, for you have not here a lasting home. To Him direct your daily prayers, your sighs and tears, that your soul may merit after death to pass in happiness to the Lord.