I wonder about the issue of sining with the hope that you can repent tomorrow.
 Other than the fact that you may not live to tomorrow, is there any other danger in it?
  I am confused. Those who believe in the existence of hell still sin, so I conclude that any mortal sin we (who believe in God) commit is mixed with the thought "I will repent tomorrow", otherwise we would never sin mortally and risk going to hell.
  Am I right?

  So any mortal sin that a faithful commits is twofold, one is the sin itself and the other is the presumption or despair that is mixed with it.  
   I read that it took St. Augustine 12 years to get rid of a sin. I cannot imagine that all those years he was falling into sin and weeping alot in confession the next day.

I have typed up Chapter 26 of The Sinner's Guide, by Venerable Louis of Granada. The copyright is from 1883. As far as I am aware the Typography by TAN books, which cannot be reproduced without permission, does not equal the text itself but the copying of the text in the format that it has been digitally reset. So I'm not allowed to scan it, but typing it is fine. If not, then Matthew can just delete this post.

I got info from here:

http://ahds.ac.uk/copyrightfaq.htm

27. What are the implications of digitising a work by an out of copyright author, but from a modern printed edition of the work?

Answer
The literary work is out of copyright but the typography (the layout of the book) will be protected by copyright. Typography of books comes under the classification of 'Published Editions'. So whilst digitising the text is not infringing any copyright, digitising from the modern printed edition will. Thus you could be sued for infringing copyright. In these instances it would be better to find an edition that is out of copyright and digitise from this. An alternative would be to just type in the text and save as a text file.

However, I insist everyone should buy this book.

Chapter 26:

Of those who Continue in Sin, trusting in the Mercy of God

Besides those who defer their conversion till the hour of death, there are others who persevere in sin, trusting in the mercy of God and the merits of His Passion. We must now disabuse them of this illusion.

You say that God's mercy is great, since He died on the cross for the salvation of sinners. It is indeed great, and a striking proof of its greatness is the fact that He bears with the blasphemy and malice of those who so presume upon the merits of His death as to make His cross, which was intended to destroy the kind om of evil, a reason for multiplying sin. Had you a thousand lives you would owe them all to Him, yet you rob Him of that one life which you have and for which He died. This crime was more bitter to Our Saviour than death itself. For it He reproaches us by the mouth of His prophet, though He does not complain of His sufferings: "The wicked have wrought upon my back; they have extended their iniquity (Psalms 128:3).

Who taught you to reason that because God was good you could sin with impunity? Such is not the teaching of the Holy Spirit. On the contrary, those who listen to His voice reason thus: God is good; therefore, I must serve Him, obey Him, and love Him above all things. God is good; therefore, I will turn to Him with all my heart: I will hope for pardon, notwithstanding the number and enormity of my sins. God is good; therefore, I must be good if I would imitate Him. God is good; therefore, it would be base ingratitude in me to offend Him by sin.

Thus, the greater you represent God's goodness the more heinous are your crimes against Him. Nor will these offenses remain unpunished, for God's justice, which protects His mercy, cannot permit your sinful abuse of it to remain unavenged. This is not a new pretext; the world has long made use of it. In ancient times it distinguished the false from the true prophets. While the latter announced to the people, in God's name, the justice with which He would punish their iniquities,. the former, speaking in their own name, promised them mercy which was but a false peace and security.

You say God's mercy is great: but if you presume upon it you show that you have never studied the greatness of His justice. Had you done so you would cry out to the Lord with the psalmist: "Who knoweth the power of thy anger, and for thy fear who can number thy wraith?" (Psalms 89:11-12). But to dissipate your illusion, let me ask you to contemplate this justice in the only way in which we may have any knowledge of it--that is, in its effects here below.

Besides the result we are seeking, we shall reap another excellent advantage by exciting in our hearts the fear of God, which, in the opinion of the saints, is the treasure and defense of the soul. Without the fear of God the soul is like a ship without ballast: the winds of human or divine favor may sweep it to destruction. Notwithstanding that she may be richly laden with virtue, she is in continual danger of being wrecked on the rocks of temptation, if she be not stayed by this ballast of the fear of God. Therefore, not only those who have just entered God's service, but those who have long been of His household, should continue in this salutatory fear: the former by reason of their past transgressions, the latter on account of their weakness, which exposes them to danger at every moment.

This holy fear is the effect of grace, and is preserved in the soul by frequent meditation. To aid you in this reflection we shall here propose a few of the practical proofs of the greatness of God's justice.

The first work of God's justice was the reprobation of the angels. "All the ways of God are mercy and justice" (Psalms 24:10), says David: but until the fall of the angels, divine justice had not been man infested. it had been shut up in the bosom of God like a sword in the scabbard, like that sword of which Ezechiel speaks with alarm, foretelling the ruin it will cause. (Ezechiel 21). This first sin drew the sword of justice from its scabbard, and terrible was the destruction it wrought. Contemplate its effects; raise your eyes and behold one of the most brilliant beings of God's house, a resplendent image of the divine beauty, flung with lighting-like rapidity from a glorious throne in Heaven to the uttermost depths of Hell, for one thought of pride (Luke 10:18). The prince of heavenly sprits becomes the chief of devils. His beauty and glory are changed into deformity and ignominy. God's favorite subject is changed into His bitterest enemy, and will continue such for all eternity. With what awe this must have filled the angels, who knew the greatness of his fall! With what astonishment they repeat the words of Isaias: "How art thou fallen from heaven, O Lucifer, who dist rise in the morning"? (Isaias 14:12).

Consider also the fall of man, which would have been no less terrible than that of the angels, if it had not been repaired. Behold in it the cause of all the miseries we suffer on earth: original and actual sin, suffering of body and mind, death, and the ruin of numberless souls who have been lost forever. Terrible are the calamities it brought upon us; and even greater would be our misfortunes had not Christ, by His death, bound the power of sin and redeemed us from its slavery. How rigorous, therefore, was the justice of God in thus punishing man's rebellion; but how great was His goodness in restoring him to His friendship!

In addition to the penalties imposed on the human race for the sin of Adam, new and repeated punishments have at different times been inflicted upon mankind for the crimes they have committed. In the time of Now, the whole world was destroyed by the deluge (Genesis 7). Fire and brimstone from Heaven consumed the wicked inhabitants of Sodom and Gomorrah (Genesis 19). The earth opened and wallowed alive into Hell Core, Dathan, and Abiron for resisting the authority of Moses (Numbers 16). Nadab and Abiu, sons of Aaron, were destoyed by a sudden flame from the sanctuary because they offered strange fire in the sacrifice (Leviticus 10). Neither their priestly character, nor the sanctity of their father, nor the intimacy with God their uncle, Moses, could obtain for them any remission for their fault.

Recall the example of Ananias and Sapphira, stuck dead by God for telling a lie ( Acts 5). But the strongest proof of the rigor of God's justice was the satisfaction required for sin, which was nothing less than the death of His only-begotten Son. Think of this Price of man's Redemption, and you will begin to realize what sin is and how the justice of God regards it. Think, too, of the eternity of Hell, and judge of the rigor of that justice which inflicts such punishment. This justice terrifies you, but it is no less certain than the mercy in which you trust. Yes, through endless ages, God will look upon the indescribable torments of the damned, but they will excite in Him no compassion; they will not move Him to limit their sufferings or give them any hope of relief. Oh! Mysterious depths of divine justice! Who can reflect upon them and not tremble?

Another subject to which I would call your serious attention is the state of the world. Reflect on this, an you will begin to realize the rigors of God's justice. As an increase in virtue is the effect and reward of virtue, so likewise an increase in sin is the effect and punishment of sin. Indeed, it is one of the greatest chastisements that can be inflicted on us, when we are permitted, through blindness and passion, to rush headlong down the broad road of vice, adding sin to sin every day and hour of our lives. This is but just; for when man once mortally sins he loses all right to any help from God. It is owing solely to the divine mercy mercy when he is converted. Look, therefore, over the world, and behold the greatness of iniquity. Think of the millions who are living in infidelity and heresy. Think how many callings themselves Christians are daily betraying their name by their scandalous lives.

Why is this sad condition permitted? Ah! It is owing to man's crimes. God is disobeyed, insulted, and mocked by the majority of men, and His long-suffering justice, being wearied by their wickedness, permits them to go on in their mad career. St. Augustine is an illustrious example of this. "I was plunged," he says, "in iniquity, and Thy anger was aroused against me, but I knew it not. I was deaf to the noise which the chains of my sins made. But this ignorance, this deafness, were the punishments of my pride."

Reflect on this. Men act freely when they sin, for no man is forced to do wrong. But when they have fallen they cannot rise without the divine assistance. Now, God owes this to no man. It is His gratuitous gift when He restores the sinner to His favor. Hence He but exercises His justice when He permits him to remain in his misery, and even to fall lower.

When, therefore, we behold so much iniquity, have we not reason to feel that God's justice permits men to become so blinded and hardened? I say permits, for man is the cause of his own miseries; God urges him only to what is good. If, then, you perceive in yourself any mark of such divine anger, be not without fear. Remember that you need no help but your own passions and the devil's temptations to carry you along the broad road to destruction. Stop while you have time. Implore the divine mercy to aid you in retracing your steps till you discover that narrow way which leads to everlasting life. Having found it, walk manfully in it, ever mindful of the justice of God, and of the terrible truth that while thousands throng the road to death, there are few who find the way to life.

Tremble for your salvation, and while always maintaining an unshaken hope, have no less fear of Hell. You have no reason to expect that God should treat you differently from other men. Bear in mind the law of his Justice, as it has been explained, and so live that you may never expose yourself to its terrible effects here and hereafter.

Be not the victim of a vain confidence which you may flatter yourself is hope, while it is naught but presumption. Rather, in the words of the Eternal Wisdom, "Be not without fear about sin forgiven, and add not sin upon sin. And say not: The mercy of the Lord is great; he will have mercy on the multitude of my sins. For mercy and wraith quickly come from him, and his wrath looketh upon sinners." (Ecclesiasticus 5:5-7). If, then, we must tremble even for sin which has been remitted, how is it that you do not fear to add daily to your crimes? And mark well these words: "His wraith looketh upon sinners"; for as the eyes of His mercy are upon the good, so are the eyes of His anger upon the wicked. And this agrees with what David says in one of the psalms: "The eyes of the Lord are upon the just, and His ears unto their prayers. But the countenance of the Lord is against them that do evil, to cut off the remembrance of them from the earth." (Psalms 33:16-17).

"The hand of God," says the inspired author of the book of Esdras, "is upon all them that seek him in goodness; and his power and strength and wraith upon all them that forsake him." (1 Esdras 8:22). Be reconciled, therefore, with God; amend your life; and then you can confidently hope for the mercy promised to His faithful servants. "Hope in the Lord and do that which is good," we are told by the psalmist; "offer the sacrifice of justice, and trust in the Lord." (Psalms 36:3 and 4:6). This is hope; any other confidence is presumption. The ark of the true Church will not save its unworthy members from the deluge of their iniquities, nor can you reap any benefit from the mercy of God if your seek His protection in order to sin with impunity.

"Men go to Hell," says St. Augustine, "through hope, as well as through despair; through a presumptuous hope during life, and through despair at the hour of death. " (De Verbo Dei, Sermon 147). I entreat you, therefore, O sinner, to abandon your false hope, and let God's justice inspire you with a fear proportioned to the confidence which His mercy excites in you. For, as St. Bernard tells us, "God has two feet, on of justice and the other of mercy. We must embrace them both, lest justice separated from mercy should cause us to despair, or mercy without justice should excite in us presumption." (In Cantica, Sermon 80).

It's not true that we always sin thinking, "I'll repent later."

Mostly, those of us who have a good will toward God, sincerely MEAN to follow His laws, but are nevertheless weak human beings, who still fall because of that weakness, as it says in the Bible...

"For I know that there dwelleth not in me, that is to say, in my flesh, that which is good. For to will, is present with me; but to accomplish that which is good, I find not. For the good which I will, I do not; but the evil which I will not, that I do. Now if I do that which I will not, it is no more I that do it, but sin that dwelleth in me.

I find then a law, that when I have a will to do good, evil is present with me. For I am delighted with the law of God, according to the inward man: But I see another law in my members, fighting against the law of my mind, and captivating me in the law of sin, that is in my members. Unhappy man that I am, who shall deliver me from the body of this death? The grace of God, by Jesus Christ our Lord."

The Sinner's Guide in its entirety can be read here: http://www.catholictradition.org/Classics/sinners-guide.htm

Well there you go! Thanks for this.

Chapter 26: Of Those Who Continue in Sin, Trusting in the Mercy of God  

http://www.catholictradition.org/Classics/guide26.htm

For the record (to clear up any possible confusion), I simply meant to say that mostly, those of good will sin by weakness... but that although we are all (even the apostles lamented it) weak, and sin out of weakness, nevertheless we are not weak as Luther thought... that is, so weak there's no point in trying to do anything about it. Rather, by the words of the gospel, we understand that we can not despair (think there's no hope for our sinful weakness). Even so, we cannot presume... we must, of course, USE the grace God sends, fighting against our weakness until our last breath.

We are weak, but the grace of God is there to help us fight against that weakness. If we are sincerely fighting against them, they'll probably be mostly venial. "Fight" is the key word, here, though. We must fight against our temptations.