Asymmetry is usual - especially when it comes to Good and evil; because Good is (roughly speaking) taking the side of God and creation - which is a positive commitment towards the divine destiny; while evil is to be opposed to these - which is negative, oppositional.
So to become permanently Good is different from becoming permanently evil - in each case 'permanent' has a qualitatively different meaning.
As I understand it; the choice to follow Jesus Christ leads through resurrection to Heaven. It is, therefore, a transformation - a transformation from this transitional, temporary, mortal embodied life, to a final, permanent, eternal embodied life.
The resurrected life entails that we are prepared to make a permanent commitment to God's creation.
The idea of eternity and permanence should not be thought to mean that Heavenly existence is some kind of unchanging stasis. I think it is better understood in the above terms as a final transformation.
After resurrection there is no further transformation: the resurrected Man is qualitatively final in form - although he can develop further, towards creative divinity.
In the resurrected condition this eternal commitment is possible in a way that is not possible on earth.
Earthly life is 'entropic', change cannot be prevented, and change tends to be degenerative (towards chaos)...
But Heavenly life is eternally self-generating - there is no entropic tendency, but instead creation is the dominant reality.
Anyway; the path to salvation is by following Jesus to Heaven; and once that has been accomplished, that situation is irrevocable.
The resurrected man has made a free and conscious choice to make a permanent, positive commitment, and that commitment is - from then onwards - permanent!
We could say (just as a model summary) that there is something like a special provision made that such a permanent commitment to Good is possible; or we could simply say that if permanent commitment to Good was not possible, then Heaven would be impossible - since (across eternity) members would all be prone to lapse and reverse; and Heaven might become hell...
The situation for evil is different. There is no 'special provision' that enables any individual to make a permanent commitment to evil. Therefore, all commitment to evil is ultimately contingent; there is no 'philosophically principled' reason that actively prevents any individual (up to and including Satan) from repenting.
But it would be an error to infer from this that repentance is in practice possible for everyone. What prevents repentance is essentially Not Wanting to Repent.
With evil, there is a kind of spiral of probabilities against wanting to repent. Unprepented sin leads to more unrepented sin (as we see from everyday observation); so that individuals get deeper then deeper into evil; and the desire to repent and live in Heavenly harmony with God's creation gets less and less - while opposition to God and creation gets more habitual and stronger.
As a person becomes more evil; he develops stronger habits of untruthfulness (lying is intrinsic to evil); he practices moral inversion - such that all possible 'evidence' is understood as confirming his existing evil assumptions.
For example, other peoples' moral concern and forgiveness is interpreted as stupidity and weakness; the misery and pain of others leads to positively-reinforcing feelings of excitement, power, sexual arousal; successful dominance leads to despising those dominated; but defeat and failure leads to resentment and plans for revenge - etc.
Whatever happens, it only serves to fuel the commitment to evil, the oppositional goals.
We talk of an evil person 'selling his soul' to Satan - but this is a process, rather than a one-off transformation like salvation.
A Man chooses to enter a path of evil; and every further choice to continue the path gets easier - while repentance (while still always theoretically possible) inflicts higher and higher costs in terms of unpleasant/ crippling feelings of remorse.
It is always easier to become more evil, and it gets more and more difficult to repent.
Thus, permanent Good is asymmetrical with permanent evil: the decision permanently to choose the side of Good being qualitatively irrevocable; while the decision to choose evil is a matter of becoming more-and-more quantitatively irrevocable - more-and-more permanent; in a positive feedback fashion: with each deviation leading to further deviation in the same direction.
