Can any sin be forgiven? (According to the teaching of the Catholic Church)

Question

I was trying to research the influence Christianity had on Hitler and Nazism, when I came across this:

Hans Frank

Frank acted as lawyer and senior official for the Nazi party and legal advisor for Hitler. He also served a tenure as Governor-General of occupied Poland for which he was convicted during the Nuremberg trials for his role in perpetrating the Jewish holocaust and found guilty of complicity in the murder of millions of Poles and Polish Jews. A former Protestant (his father was a Protestant and his mother a Catholic), he converted to Roman Catholicism after his arrest where he felt relieved at the prospect of atoning for his evil deeds.

and following this, the author mentions:

The belief that one can be saved for any atrocious act demonstrates the moral flaw of Christian doctrine.

Quotes from Hitler's Henchmen and Nazi Sympathizers

I myself am a 17 year old, and I belong to the Syrian Christian Church. Now I don't really think this issue of 'forgiving-just-about-any-sin' ever arose whenever I attended church [I was surprised actually, I'd thought the pastor would've touched that topic at some point, but apparently he hasn't), so I was kinda clueless as to where to begin. I thought of asking a few Catholic friends of mine about this, and they were like:

Well, as long as you honestly didn't realize you were doing something (terribly) wrong, and if you repent and quit doing it once you do realize it, then you'd be forgiven.

Now that may seem a little...oversimplified, but hey, we're still teenagers trying to grasp as much as possible from the Bible.

Now I don't seem to recall any direct reference to this 'ultimate absolution' anywhere in the New Testament, and as I'm not able to make any headway here, I resorted to SE.

This issue just keeps gnawing at the back of my mind.

Note-

I did read up on 'similar' questions that were asked earlier here, but none of them specify the extent to which the sins they've conjectured goes. Perhaps murdering one person would've been the limit they've envisioned; but this question deals with a far more horrific sin...the systematic murder of millions, and I'm pretty sure that might elicit a different answer. Hence a request to the Mods here: Please don't close this question, at least not yet.

EDIT 1-

I'd prefer an answer limited to the teachings of the Catholic Church towards this issue.

EDIT 2-

Now if it is true that any sin can be forgiven (In the manner as my friends have stated it); now I'm just trying to look at this from every possible (and extreme) angle, so if the following (add-on) question might seem outrageous, pardon:

Q- Having read (portions of) the Mein Kampf and coming across an endless selection of Hitler's speeches on NatGeo, the History Channel and the like, the kind of rhetoric he employs, and that too with such conviction (eg: Who says I am not under the special protection of God?) gives me the feeling that the man truly felt God 'approved' of his actions. So, assuming the man truly, truly, did not believe he was committing genocide...could someone like Hitler even be forgiven?

Answer 1

The Catholic Church does indeed believe that if the sinner fulfills certain conditions, any sin can indeed be forgiven. Paragraph 982 of the Catechism of the Catholic Church states:

There is no offense, however serious, that the Church cannot forgive. "There is no one, however wicked and guilty, who may not confidently hope for forgiveness, provided his repentance is honest." Christ who died for all men desires that in his Church the gates of forgiveness should always be open to anyone who turns away from sin.

The quotation is from the Church's first universal catechism, the Roman Catechism, which states in Article X:

No crime, however heinous, can be committed or even conceived which the Church has not power to forgive, just as there is no sinner, however abandoned, however depraved, who should not confidently hope for pardon, provided he sincerely repent of his past transgressions.

(emphasis added)

We are told to forgive and keep forgiving (Matthew 18:21–22); how much more can God forgive! And just as God can forgive any sin, so the Church, to whom He has delegated this power, has the ability to do the same.

However, the process isn't as simple as just saying "I'm sorry" and leaving it at that. The Catechism explains:

Jesus' call to conversion and penance, like that of the prophets before him, does not aim first at outward works, "sackcloth and ashes," fasting and mortification, but at the conversion of the heart, interior conversion. ... a radical reorientation of our whole life, a return, a conversion to God with all our heart, an end of sin, a turning away from evil, with repugnance toward the evil actions we have committed. At the same time it entails the desire and resolution to change one's life, with hope in God's mercy and trust in the help of his grace. This conversion of heart is accompanied by a salutary pain and sadness which the Fathers called animi cruciatus (affliction of spirit) and compunctio cordis (repentance of heart).

(paragraphs 1430–31)

The beginning of conversion is a rejection of one's previous life—not because one feels that one ought, or because one is afraid of consequences (secular or sacred), but because one sees how sin affects one's relationship with God. This rejection and sorrow for one's sins, and determination not to sin again, is called contrition; without it one cannot be forgiven of serious sins (such as the ones you describe).

Beyond contrition, the sinner must also recognize that his actions have injured others—perhaps emotionally, or physically, or spiritually. In order to completely repair his relationship with them and with God, he is required to expiate his sin; that is, to do something to make up for the harm he has caused.

Many sins wrong our neighbor. One must do what is possible in order to repair the harm (e.g., return stolen goods, restore the reputation of someone slandered, pay compensation for injuries). Simple justice requires as much. But sin also injures and weakens the sinner himself, as well as his relationships with God and neighbor. Absolution takes away sin, but it does not remedy all the disorders sin has caused. Raised up from sin, the sinner must still recover his full spiritual health by doing something more to make amends for the sin: he must "make satisfaction for" or "expiate" his sins. This satisfaction is also called "penance."

The penance the confessor imposes must take into account the penitent's personal situation and must seek his spiritual good. It must correspond as far as possible with the gravity and nature of the sins committed. It can consist of prayer, an offering, works of mercy, service of neighbor, voluntary self-denial, sacrifices, and above all the patient acceptance of the cross we must bear. Such penances help configure us to Christ, who alone expiated our sins once for all.

(Catechism paragraphs 1459–60)

In a case such as you suggest, I suppose that a prison sentence imposed by secular authorities might be part of penance for this sin. It will also involve prayer and perhaps other works of mercy aimed at helping re-establish the sinner's relationship with God.

Given the presence of contrition, though, and a humble willingness to perform the imposed penance, any sin can be forgiven by God and thus by His Church. This is true even if the sinner knew for certain that what they were doing was sinful. God's mercy extends not just to those who did wrong out of ignorance, but to those who knew what they were doing—provided they are contrite and sincerely desire to amend their life.

Answer 2

"The special grace of the sacrament of the Anointing of the Sick has as its effects: the uniting of the sick person to the passion of Christ, for his own good and that of the whole Church; the strengthening, peace, and courage to endure in a Christian manner the sufferings of illness or old age; the forgiveness of sins, if the sick person was not able to obtain it through the sacrament of penance; the restoration of health, if it is conducive to the salvation of his soul; the preparation for passing over to eternal life" (CCC 1532).

http://www.catholic.com/tracts/anointing-of-the-sick

Canon 1005 This sacrament is to be administered when there is a doubt whether the sick person has attained the use of reason, whether the person is dangerously ill, or whether the person is dead.

http://www.vatican.va/archive/ENG1104/_P3M.HTM

Let's take the Hitler example.
Hitler committed a lot of sins. It is believed that he also committed suicide, a mortal sin after which you can't confess -- because you're dead.

However, there's a couple of things that should be established:

• A sacrament administered by a priest is infallible. Once administered, it comes into full effect. Holy sacraments cannot "fail".
• Clinical death is not the same as actual death. There's a not-so-brief moment between shooting yourself in the head, and actually dying.
• There exists the possibility that Hitler, in his last moment, repented his sins right after pulling the trigger, and feared the judgement of God and asked for forgiveness -- even though he couldn't express himself because he had just blown his head off.

So if, right after Hitler commiting suicide (a mortal sin), a priest had administered the sacrament of Anointing of the Sick to (now clinically dead) Hitler, he would've been effectively pardoned of all his sins including suicide.

That is the argument I've most often heard regarding Catholics being "lucky" because they can live a life of sin, die peacefully in their beds, and still go to Heaven, if a priest is kind enough to administer the sacrament that forgives all their sins because he thinks they repented last minute.

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EDIT: The above answer is based on the second point mentioned: difference between clinical death and actual death.

Sometimes, people would shoot themselves in the head, or jump from a balcony 10 stories high, and not die but just fall into a comma with their vitals greatly diminished. Anybody but a doctor would think they're dead when they're not. Even doctors would now and then declare some person with no brain activity as "clinically dead", only for the person to come back to life afterwards, which means they weren't actually dead -- not for God at least.

So a priest, being absolutely convinced that the person is both repented and not actually dead, can still administer the sacrament in good faith. Even if they cannot receive the Viaticum.

Now to the personal anecdote: I myself have witnessed this sacrament being administered to people which were, by all human standards, dead. A sudden cardiac arrest here, a life support disconnection there. Pious people that actively participated with the community, true; but still dead people.
However, the priest chose to believe that they repented last minute, and that their soul hadn't yet parted to meet God, and thus the oil was given and their sins were cleared, because of point 1.