The greater number of mankind employ their time badly; many others  are perfectly embarrassed by their time and do not know how to employ it; their sole object is to fritter it away, to pass it agreeably to themselves, or at least without feeling themselves wearied and bored. Do they ever succeed in this? No. Experience teaches us that those people who are most greedy for pleasure are soon satiated with it, and that disgust, wariness, and idleness soon render them unbearable, even to themselves. But unfortunately, when they have acquired this experience, it is very rarely that they profit by it; the bad habits are formed; it would cost too much to adopt good ones. They continue to live as they have lived, although they no longer flatter themselves with the hope of happiness they once confidently expected. Woe to those who abuse and misuse their time! One day they will regret having acted so, but then their regrets will be in vain!

Our Use Of Time Will Determine Our Eternity

What is time, with regard to myself? It is my present and actual existence. Past time, or my past existence, is no longer anything, as far as I am concerned; I can neither recall it nor change anything in it. The time to come, or my future existence, has not yet arrived, and perhaps never will arrive. It does not depend on me; I cannot count on it; and the most powerful monarch in the world cannot make sure of one single instant of life.

No one is ignorant of these two simple truths, but very few draw from them the conclusions they ought to draw. It is true and certain that I have only the present moment, which cannot be divided, which nothing can fix, not even thought, and which is passing away with a rapidity that nothing can equal. The present moment, or is this actual existence - from whom do I hold it? From God. It is He who called me from nothing into being. It is He who has preserved my existence from one instant to another, and who is preserving it at this present moment. Will He preserve it for me in the moment that shall immediately follow this one? I do not know; and nothing in the world can give me the assurance of it.  

Why has time been given to me? So that by it I may merit a happy eternity. I shall live forever; faith teaches me this; my reason even assures me of another life. The desire of immortality is implanted in the depths of my heart, and this desire, which God Himself has planted there, can never be frustrated of its object.  I am, then, born for eternity, but this eternity will be happy or wretched, according to the use I make of time. If I sincerely repent of the bad use of time I have made in the past, if I am beginning to make a good use of it, if I persevere in this good use until the moment comes when time shall cease for me, I shall be eternally happy. If I have made a bad use of time, and since neither the past or the future is in my own power, it is quite true to say that my eternity depends always on the present moment.

Now, at this present moment, what is my state? Would I like to die just as I am now? Would I dare to run the risk of my eternity just as I am now? If I would not, am I not a fool to remain in the state I am in, to count on the future, when I am not sure of the moment that shall follow this one, when perhaps between me and eternity there is only one instant of time?

An excerpt from The Spiritual Life by Fr. Jean Nicholas Grou

On The Zealous Amendment Of Our Life.

Be watchful and diligent in the service of God, and frequently consider why you are come here, and why you have renounced the world. Was it not that you might live to God, and become a spiritual man? Endeavor then, to make progress, and you will soon receive the reward of your labors; then neither fear nor sorrow will be able to trouble you. Labor for a short while now, and you will find great peace of soul, and everlasting joy. If you remain faithful in all your doings, be sure that God will be faithful and generous in rewarding you. Keep a firm hope that you will win the victor's crown; but do not be over confident, lest you become indolent and self-satisfied.
The Imitation of Christ. Page 63.

Since we know neither the day nor the hour, we should follow the advice of the Lord and watch constantly so that, when the single course of our earthly life is completed, we may merit to enter with him into the marriage feast and be numbered among the blessed, and not, like the wicked and slothful servants, be ordered to depart into the eternal fire, into the outer darkness where "men will weep and gnash their teeth."
Catechism #1036.