Referring to the fall of Satan and his angels, according to the Catechism:
393 It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels' sin unforgivable. "There is no repentance for the angels after their fall, just as there is no repentance for men after death."
Can someone please explain further why the angels who turned away from God cannot be forgiven, unlike man? What does irrevocable character of their choice mean?
Satan and all the fallen angels (demons) are completely consumed with evil and chose to do evil with all their intellect and sin against God, thus repentance is no longer possible for them.
According to Canon 1 of the VI Lateran Council in 1215, the fallen angels were good. Does any goodness still exist within these demons and can they repent since God is merciful to sinful humans who repent of their evil? According to the teaching of the Catholic Church, no. There is not good left within Satan and his angels and they are completely consumed by evil. As a result of this and because they chose to sin against God with their full intellect and will. As Paragraph 393 of the Catechism of the Catholic Church states:
It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels' sin unforgivable. "There is no repentance for the angels after their fall, just as there is no repentance for men after death." - The Catholic Teachings On The Angels - Part 2: The Fall Of Satan
Before the death of a human being, man is able to repent of past sins, but not after death.
Why does the soul become immutably fixed, in good or in evil, immediately after death can be read about here: IMMUTABILITY AFTER DEATH.
My understanding is that since angels' intellect is more refined than ours, angels do not change their minds, and are not indecisive. Once they decide, they decide for eternity. The "irrevocable character of their choice" would then refer to the nature of angels' intellect being more aligned with their wills.
Daisy gave a good answer which aligns with a great insight given by the honorable, deceased Catholic Bishop Fulton Sheen.
In his book "Your Life Is Worth Living", Sheen emphasizes that: "When an angel decides anything, it sees all of the consequences of its acts with perfect clarity. The principle of contradiction is that a thing cannot be, and be, at one and the same time and under the same formal circumstances. You can never go back on the principle of contradiction. An angel sees the consequences of all its resolutions and choices just as you see that principle. You can never take the principle of contradiction back; it's part of your mental life. When an angel chose to rebel against God, to make itself God, to deny love, it made pardon forever impossible..."
The fallen angels, in light of the "Principle of Contradiction", can never go back to the Goodness they blasphemed. They are beyond space and time, always present in the decision they made.... FOREVER....
Sheen goes on to expound why it is different for humans. "With you and me, it's a little different. We do not always see the effects of our decisions. Our mind is darkened our intellect is weakened, and our will is poor in its resolutions; God allows pardon."
Moreover, as to why the current Angels never fall, it is Traditionally asserted that the Angels, in light of the Glory of God they were bathed in, were all given a one time decision to obey God... Thus, they were confirmed eternally according to their decision either to Eternal Glory or Eternal Damnation.
Angels, like God, eternally live in the Present; unlike humans. Thus,the Principle of Contradiction applied in the perpetual Present sense cannont allow a thing to be and not to be at the same time. Thus, the Angels, prior to eternal confirmation, who chose to disobey God in the Present will always remain in that Present, irrevocable state. This is not true for humans who still have the gift of free will and a future......
