What is mortal sin?

[Lorenzo]

 Q. What is mortal sin?

[Lorenzo]

Answer: Mortal sin is a grievous transgression of the law, whether this grievousness arises from the nature of the thing done, or from the circumstances in which it is done, or from the will of the law given who strictly requires the observance of what is commanded as was the sin of our first parents in eating the forbidden fruit.

[Lorenzo]

 Q. What are the effects of mortal sin?

[Lorenzo]

 Answer: It banishes the grace of God from our souls, renders us hateful and abominable in the sight of God, and worthy of eternal punishment. For th is reason it is called mortal, because it kills the soul in this life, by depriving it of the sanctifying grace of God, which is the spiritual life of the soul, and condemns us to eternal death in the life to come.

[Lorenzo]

 Q. Is mortal sin a great evil?

[Lorenzo]

 Answer: It is the greatest of all evils, because infinitely opposed to the infinite goodness of God. It is a bottomless pit, which o created understanding can fathom; for as none but God himself can fully comprehend his own infinite goodness, so none but God himself can perfectly comprehend the infinite malice and enormity that is found in th is opposite evil. It is the parent both of the devil and of hell; for hell was only made for mortal sin, and Lucifer was an angel of light till he was transformed into a devil by mortal sin.

[Lorenzo]

From what does the malice of mortal sin chiefly appear?

[Lorenzo]

From what does the malice of mortal sin chiefly appear?

A. From several important considerations;

1. From the greatness of the injury done to God;

2. From the hatred with which God adhors it;

3. From the severity with which he punishes it, even in this world;

4. From the ingratitude it contains against Jesus Christ;

5. From the sad effects it produces in our souls in this life; and,

6. From the loss of heaven, of which it deprives us, and the torments of hell to which it condemns us, in the life to come.

[Lorenzo]

Reference:
http://www.catholicdoors.com/teaching/book1/1-16.htm#16b