Axiom: The human person needs to go beyond beyond natural limits.
As evidence, start with II Republic where Socrates is forced to re-imagine his idea of a city after it is ridiculed as “A city for pigs”, i.e. one limited to meeting what fell within natural human needs for nourishment, sheltering, health, recreation, etc. The critique was on-point: while pigs are perfectly content (or even in a state of bliss) when their natural needs are met, humans have a need for the heroic, the glorious, the illustrious, magnanimous; or on a more basic level for the refined, luxurious, elegant, etc. This is why we can identify ancient humans by jewelry, large decked-out temples, well-executed art… one is not sure he’s found a fully human species if they merely have tools like controlled fire or sharpened rock-axes.
Since we don’t have any choice whether we want to go beyond the limits of nature, the only question is how we will do so. I’ll focus on one way in which we want to go beyond limits, sc. the moral limits of human behavior.
One approach is to go beyond nature by contradicting it. Raising kids makes it clear that even before we are fully self conscious we defy the rules that restrain us as a proof of our own self-sufficiency. Augustine gives the classic description of this in his analysis of his desire to steal pears. From within this perspective, rules are at best useful illusions for living together, though the clever and wise seek ways to flout them. This flouting doesn’t require that my life be outwardly rebellious or defiant in any obvious way, but only that, somewhere in my heart, I have made a definitive judgment that some moral rule does establish a limit I am bound to respect. To return to Augustine’s life, it’s enough to steal some pears in the dark.
The only other approach has to preserve the limits of human nature. But this seems impossible: how can we preserve the natural limits of our nature while being true to our desire to transcend all limits?
The Platonic-Christian answer is that staying within the limits can be in part rewarded by the gift of transcending them. The moral limits of life are tied to a larger story culminating in the possibility of transcending all limits by way of divine gift. The possibility of rewards also raises the possibility of punishments, perhaps even perpetual ones.
In Christian dogma, these two ways of transcending moral limits are, respectively, mortal sin and sanctifying (or diefying) grace.