There was a famous correspondance in The Times under the title of ‘What’s wrong with the world?’ Probably the most penetrating of all the letters was from G.K. Chesterton:
Dear Sir
I am
Your sincerely,
G.K. Chesterton.
That is precisely the answer. The heart of the human problem is the problem of the heart. People have a variety of theories about ‘what is wrong with the world?’ but no one can truthfully answer the question until he can say eith honesty, ‘Dear Sir, I am.’
Christ described human nature in these words; ‘From the inside , out of man’s heart come evil thoughts, acts of fornication, of theft, murder, adultery, ruthless greed and malice; fraud, indecency, envy, slander, arrogance, and folly; these evil things all come from inside, and they defule a man. (Mk 7:21-23)
David Watson, My God is Real, p26

I went to the psychiatrist to be psychoanalysed
To find out why I killed the cat and blackened my husband’s eyes.
He laid me on a downy couch to see what he could find,
And here is what de dredged up from my subconscoius mind:
When I was one, my mommie hid my dollie in a trunk,
And so it follows naturally that I am always drunk.
When I was two, I saw my father kiss the maid one day,
And that is why I suffer now from kleptomania.
At three, I had the feeling of ambivalence towards my brothers,
And so it folllows naturally I poison all my lovers.
But I am happy; now I’ve learned the lesson this has taught;
That everything I do that’s wrong is someone eals’s fault.
Drive the point home, G Twelftree, p 174

A Slav folk tale tells the story of men who once visited a holy man to ask his advice. “We have done wrong actions,” they said, “and our consciences are troubled. What must we do to be forgiven?”
“Tell me of your wrong doings my sons,” said the old man.
The first man said, “I committed a great and grevious sin.”
“I have done a number of wrong things,” said the second man, “but they are all quite small, and not at all important.”
“Go,” said the holy man, “and bring me a stone for each misdeed.”
The first man staggered back with an enormous boulder. The second cheerfully brought a bag of small pebbles.
“Now,” said the holy man, “go and put them back where you found them.”
The first man shouldered his great rock again, and staggered back to the place from which he had brought it. But the second man could only remember where a very few of his pebbles had lain. He came back saying that the task was too difficult.
“Sins are like those stones,” said the old man. “If a man has committed a great sin, it lies like a heavy stone on his conscience; yet if he is truly sorry, he is forgiven and the load of guilt is taken away. But if a man is constantly doing small things that he knows to be wrong, he does not feel any great load of guilt, and so he is not sorry, and remains a sinner. Do you see, my sons, it is as important to avoid little sins as big ones.”
1500 Illustrations for Preaching & Teaching – Pub Marshall Pickering

“Sin is the most expensive thing in the universe… If it is forgiven sin, it cost God His only Son… If it is unforgiven sin, it cost the sinner his soul and an eternity in hell.”
Charles G Finney – Quoted from A Box of Delights J. John & Mark Stibble

“Take this rule: whatever weakens your reason, impairs the tenderness of your conscience, obscures your sense of God, or takes off your relish of spiritual things; in short, whatever increases the strength and authority of your body over your mind, that thing is sin to you, however innocent it may be in itself.”
Susanna Wesley – Letter to her son John Wesley – June 8, 1725