A person often forgets the sins he committed, but there may be certain unforgettable sins.
David the Prophet for instance asked the Lord in his prayer to forget his many sins, saying, "If You, Lord, should mark iniquities, O Lord, who could stand?" (Ps 130: 3) "Do not enter into judgment with Your servant, for in Your sight no one living is righteous." (Ps 143: 2) "Do not remember the sins of my youth, nor my transgressions." (Ps 25: 7) Even concerning his errors, he says, "Who can understand his errors? Cleanse me from secret faults." (Ps 19: 12)
However, there was a certain sin which he could not forget about which he said, "My sin is always before me." (Ps 51: 3)
It left a deep impact on his emotions and memory, and shook him strongly, so he said, "I am weary with my groaning; all night I make my bed swim; I drench my couch with my tears." (Ps 6: 6)
Samson likewise committed many sins, but the most serious sin that shook him all through and he could not forget was revealing his secret to Delilah. It made him break his vow, and his enemies conquered him, put out his eyes, and made him a grinder in prison (Judges 16).
Like David and Samson was Solomon.
He sank deeply in worldly pleasures with peace of mind and conscience (Eccl 2: 9, 10). Then he committed his big sin, which made God angry with him (1 Kgs 11: 9- 13), by going after Ashtoreth the goddess of the Sidonians and Milcom the abomination of the Ammonites, and built a high place for Chemosh the abomination of Moab and for Molech the abomination of the people of Ammon (1 Kgs 11: 5- 7). Solomon did not forget this sin, nor did God forget it, for God inflected punishments on him, saying, "If he commits iniquity, I will chasten him with the rod of men and with the blows of the sons of men." (1 Sam 7: 14) To chastise him, God set adversaries against him, Hadad the Edomite, Rezon the son of Eliadah, Jeroboam the son of Nebat (1 Kgs 11: 14- 26).
A girl, for instance, may fall in sin with a young man and wakes up late.
With a sleeping conscience, the sin may seem simple, but she will wake up to find that she has lost her virginity or even conceived of a child. She may think of abortion and murder of the baby, but as this needs money, which she does not have, she falls in many lies! It is a big unforgettable sin implanted deep in her mind!
A fault may even destroy one's whole life.
A student who cheats in the exam will be dismissed from the university, and will be exposed to disdain and bad reputation! A person who falls in drug addiction, will have his nerves and name destroyed, even after being healed! More serious is the state of a person who contracts AIDS through sin. Seeing his health destroyed and death is nearby, he cries within blaming himself for such a fall, but very late!
The sin of Adam and Eve had its effect on all mankind, with all the serious consequences that continued for generations.
Their sin caused the corruption of the whole human nature, and needed the Incarnation and the Redemption. It was so serious that God let its effects continue until now. God said to Adam, "In the sweat of your face you shall eat bread till you return to the ground, for out of it you were taken; For dust you are, and to dust you shall return." And to Eve He said: “I will greatly multiply your sorrow and your conception; In pain you shall bring forth children." (Gen 3: 16- 19)
These consequences continue until now, in spite of the attempts of man to overcome them!
Some sins caused the perdition of those who committed them.
Some perished in their sins, like Judas Iscariot. Undoubtedly, he had many sins, as being a thief, and stealing from the money-box that was with him (Jn 12: 6)!
However, the biggest sin which he could not bear and made him hang himself was his dishonesty to his Master! (Mt 27: 5)
A similar sin was that of the sons of Eli the Priest, for which the Lord said, "The iniquity of Eli’s house shall not be atoned for by sacrifice or offering forever." (1 Sam 3: 14) In anger the Lord judged Eli himself for the iniquity of his sons which he was aware of, but did not restrain them (1 Sam 3: 13).
Another similar sin was that of Ananias and Sapphira his wife, by which they deserved to die immediately without any chance for repentance (Acts 5)!
Other sins extended for long generations.
An example is the curse of Canaan by our father Noah because of disdaining his father (Gen 9: 25). It continued until the days of the Lord Christ and He used it in His talk with the Canaanite woman (Mt 15: 26). Another example is the punishment to those who, led by pride and arrogance, built the Tower of Babel. The Lord's punishment was confusing their language (Gen 11: 7), which punishment continued up to the present day.
Many sins are not recorded in the Holy Scripture, but it is generally said, "They have all turned aside, they have together become corrupt; There is none who does good, no, not one." (Ps 14: 3)
On the other hand, certain sins and their punishments are recorded in the Scripture, such as:
The adultery committed by the whole creation which led to the flood (Gen 6); the homosexuality that led to the destruction of Sodom (Gen 19); the attempt to steal priesthood by Korah, Dathan, and Abiram for which the earth opened its mouth and swallowed them up (Num 16); the dishonesty of Absalom to his father David (1 San 6- 18); the denial of Peter and the Lord's forgiveness to him (Mt 26; Jn 21); the desire of Ahab for the vineyard of Naboth the Jezreelite (1 Kgs 21); the worship of idols by Jeroboam the son of Nebat, Ahab, and others ( Kgs 12); and many other unforgettable sins, some of which even were committed by prophets.
Saul of Tarsus, as an example, never forgot that he had persecuted the church, although he had done this by ignorance before believing in Christ, and although he repented and became an elect apostle who did many wonders and signs and labored much for the sake of spreading the gospel message. He said about himself, "Although I was formerly a blasphemer, a persecutor, and an insolent man; but I obtained mercy because I did it ignorantly in unbelief." (1 Tim 1: 13) He mentioned his sin again when speaking about the appearance of the Lord Christ to him after His resurrection, "Last of all He was seen by me also, as by one born out of due time, for I am the least of the apostles, who am not worthy to be called an apostle, because I persecuted the church of God." (1 Cor 15: 8, 9)
The seriousness of sins lies not in their number, but in their awfulness.
The sin of Simon the sorcerer, though not repeated, was a serious sin, because he wanted to purchase the gift of God with money! (Acts 8: 18- 30) Likewise was the sin of Herod, who accepted the words of the people 'The voice of a god and not of a man!' An angel of the Lord struck him immediately, because he did not give glory to God, and he was eaten by worms and died (Acts 12: 22, 23).
Peter's sin of denial was not repeated, but its seriousness was in its weight, because sins are not counted but weighed.
If to its weight is added its repetition, the matter will be more serious. Such sins lie in the subconscious and deepen their roots turning into a source of dreams, thoughts, and lusts. They become a nature in man, and a habit sticking to man's nature as part of his personality, hard to get rid of.
It is like something one tastes and likes, so cannot dispense with!
One in such a case is ready to repent for all one's sins except for this one sin! It is flowing in his blood, deep in his emotions and desires. However, some do not forget their sins because they trouble their conscience when repenting, therefore they groan with much pain exclaiming how they reached such a state and dropped to such a level. Others remember their big sin while still captive to it, unable to resist, which is harder!
Such a person needs a great push from outside that may rescue him from the pit in which he has fallen, and that may tear up the ties binding him.
He needs the work of the grace and of God's Holy Spirit in order to hate such a sin and be no more attracted to it.
Other sins may trouble a person and shake his conscience when he wakes up.
Examples of such a sin are the sin of apostasy, blasphemy, and doubt. Yea, for doubt easily enters man's mind and hardly comes out. It makes a person lose the simplicity of faith that he had before and get lost in endless intellectual matters. If doubts concern somebody, a person will lose forever trust in him.
Some other sins are unforgettable because of their consequences.
If a husband, for instance, abused his wife and she could not bear it, she might leave him and go to her parents' home. Any reconciliation attempts may be for no avail because the insult was deep. She may lose her love for him and form a bad idea about his character and way of dealing. He will remember that fault with regret, considering it the biggest sin in his marital life. The matter may develop more seriously to reach courts.
A sin may become the biggest sin in one's life if it is irremediable.
If a monk, for instance, got married breaking his vow, and lost his virginity and his good reputation, and his priesthood if he was a priest, he would not be able to restore all this. Imagine if this monk lost his wife or differed with her, he will find himself in complete loss spiritually, bodily, socially, and dogmatically!
Sometimes a person's biggest sin is due to a defect in him, like the love of getting news about the others, which thing may cause him to lose his friends and the others. Such a person craves for news, searches for them, asks others and listens stealthily, then makes conclusions. He may even address embarrassing questions to get some news out of the answer. He may exchange news with others like him. Finally, he finds himself bearing a big and heavy burden of news, so he turns into a news conductor!
Such a person makes of the others news the talk of everybody, to appear as if he knows all secrets and is an object of trust.
People may hear such secrets, but some may avoid him lest they hear something spiritually harmful, or become themselves an object of his news. He will find nobody around him, and troubled by his thoughts, he will lose trust in everybody.
Again, he may turn from a news conductor to a news inventor!
The hardest sin indeed is that which sticks to a person more than skin to flesh. It becomes like part of his nature and character. It may turn into a psychic disease within him causing other perhaps incurable diseases, whether ethical or social.