For the sake of discussion (and context):
'He who from among these angelic powers was set over the earthly realm, and into whose hands God committed the guardianship of the earth, was not made wicked in nature but was good, and made for good ends, and received from his Creator no trace whatever of evil in himself. But he did not sustain the brightness and the honour which the Creator had bestowed on him, and of his free choice was changed from what was in harmony to what was at variance with his nature, and became roused against God Who created him, and determined to rise in rebellion against Him: and he was the first to depart from good and become evil. For evil is nothing else than absence of goodness, just as darkness also is absence of light. For goodness is the light of the mind, and, similarly, evil is the darkness of the mind. Light, therefore, being the work of the Creator and being made good (for God saw all that He made, and behold they were exceeding good) produced darkness at His free-will. But along with him an innumerable host of angels subject to him were torn away and followed him and shared in his fall. Wherefore, being of the same nature as the angels, they became wicked, turning away at their own free choice from good to evil.
Hence they have no power or strength against any one except what God in His dispensation hath conceded to them, as for instance, against Job and those swine that are mentioned in the Gospels. But when God has made the concession they do prevail, and are changed and transformed into any form whatever in which they wish to appear.
Of the future both the angels of God and the demons are alike ignorant: yet they make predictions. God reveals the future to the angels and commands them to prophesy, and so what they say comes to pass. But the demons also make predictions, sometimes because they see what is happening at a distance, and sometimes merely making guesses: hence much that they say is false and they should not be believed, even although they do often, in the way we have said, tell what is true. Besides they know the Scriptures.
All wickedness, then, and all impure passions are the work of their mind. But while the liberty to attack man has been granted to them, they have not the strength to over master any one: for we have it in our power to receive or not to receive the attack. Wherefore there has been prepared for the devil and his demons, and those who follow him, fire unquenchable and everlasting punishment.
Note, further, that what in the case of man is death is a fall in the case of angels. For after the fall there is no possibility of repentance for them, just as after death there is for men no repentance.'
Source: Saint John Damascus, De Fide Orthodoxa (Book II, Chapter IV).
'II. THE FALL OF THE ANGELS
391 Behind the disobedient choice of our first parents lurks a seductive voice, opposed to God, which makes them fall into death out of envy.266 Scripture and the Church's Tradition see in this being a fallen angel, called "Satan" or the "devil".267 The Church teaches that Satan was at first a good angel, made by God: "The devil and the other demons were indeed created naturally good by God, but they became evil by their own doing."268
392 Scripture speaks of a sin of these angels.269 This "fall" consists in the free choice of these created spirits, who radically and irrevocably rejected God and his reign. We find a reflection of that rebellion in the tempter's words to our first parents: "You will be like God."270 The devil "has sinned from the beginning"; he is "a liar and the father of lies".271
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."272
394 Scripture witnesses to the disastrous influence of the one Jesus calls "a murderer from the beginning", who would even try to divert Jesus from the mission received from his Father.273 "The reason the Son of God appeared was to destroy the works of the devil."274 In its consequences the gravest of these works was the mendacious seduction that led man to disobey God.
395 The power of Satan is, nonetheless, not infinite. He is only a creature, powerful from the fact that he is pure spirit, but still a creature. He cannot prevent the building up of God's reign. Although Satan may act in the world out of hatred for God and his kingdom in Christ Jesus, and although his action may cause grave injuries - of a spiritual nature and, indirectly, even of a physical nature- to each man and to society, the action is permitted by divine providence which with strength and gentleness guides human and cosmic history. It is a great mystery that providence should permit diabolical activity, but "we know that in everything God works for good with those who love him."275 '
Source: Catechism of the Catholic Church (Part I, Section II, Chapter I, Article I, Paragraph VII)