Tatum:
The seriousness of a sin depends on two factors.
The objective nature of the conduct (eg breaking the Commandments) and the degree of culpability.
The most serious sin is that which objectively breaks the Commandments and is also fully imputable (mortal sins).
That does not mean that breaking of the Commandment with less than full culpability is not still serious. “Serious” is about more than just losing sanctifying grave just as walking on a tightrope between two skyscrapers is still a deadly business even if one has not yet fallen.
Therefore the term “grave sin” refers to seriousness that does not always involve full culpability but is still very risky.
I would like to know from what Magisterial Document you got all this.
It is the ancient tradition of the Church used to train Priests for 900 years since Aquinas systematically formulated it. It is the framework behind the CCC and explicit in the three font model of human acts which refer to the gravity of sin being primarily determined by the object matter of the sin. Here is where Aquinas states so plainly:
“Ergo gravitas peccatorum differt secundum obiecta” Summa, I, II, 73, 3.
Breaking of the Commandments with less than full culpability is also rightly judged “serious” and “grave” because the gravity of a sin is primarily judged by reason of its matter then by degree of culpability.
We all get it that specific individuals may not be fully culpable. But “seriousness” is generally a matter of objective judgement re the matter of a sin (grave sin or not) not subjective culpability (mortal or venial sin) in individual cases.
Your above quote from JPII’s Apostolic Exhortation is making this very point but you did not understand it and only quoted half of the paragraph. Leave out the fluff and it looks like this:
“Considering sin from the point of view of its “matter” … [these] are linked with the idea of the gravity of sin’s objective content. Hence… grave sin is in practice identified with mortal sin.”
In other words we may consider grave sin and mortal sin as being the same when we focus on “the matter” (that is the object font of sin).
So when we do not focus on “culpability” (full knowledge/full consent) but focus on the object of sin then we can treat grave sin and mortal sin as practically being the same.
In which case the seriousness of grave/mortal sin in this context is due to the matter not the intent (ie culpability).
Therefore when we are advised to bring all “grave sins” to Confession that we are conscious of it seems clear this consciousness is not primarily about what we think of our personal culpability at all.
Its really about how seriously we broke God’s objective Law (the “matter” of sins). The lists of Commandments and Capital sins are the traditional guide in this area.