Recall Definition of angel = a spiritual, personal, and immortal creature, with intelligence and free will, who glorifies God without ceasing and who serve God as a messenger of his saving plan, surpassing in perfection all visible creatures.
Devil= Purely spiritual beings, who after being created by God and endowed with grace, freely failed to respond to God’s love and turned away from Him (2 Pt 2:4; Mt 25:41; Jude 6).
Lucifer (Latin lux, light and ferre to carry) is known as Satan after his rebellion. Satan one of the seraphim, the highest choir of angels who see and adore God directly.
Cast from heaven from revolting against God , some theologians consider him to be the greatest of angel before his fall. According to Christian Tradition, their sin was one of pride: They preferred to usurp or claim as their own a likeness to God that only could be received as a gift. As purely spiritual beings who do not require time and reflection to come to knowledge and decision, their refusal of God’s love was irrevocable. Their situation is comparable to the post-mortem state of unrepentant human sinners.
#393 It is the irrevocable character of their (demons) choice, and not a defect in the infinite divine mercy, that makes angels’ sin unforgiveable. “There is no repentance for the angels after their fall, just as there is no repentance for men after death.”
The power of Satan though great because he is pure spirit is not infinite. He cannot prevent the buildup of God’s reign. It is a great mystery that God would permit diabolical activity, but we know that in everything God works for good with those who live him. (Rm 8:28)
Paradiso Dante Hell was a very cold place, devoid of love, burning fire, heat of God.
Neither angels or demons can read out thoughts, though they can make good guesses based on observable actions. Reading hearts/thoughts is reserved to God alone. However, we of our own free will may ask God to let our Guardian Angels and other angels know our thoughts so as to follow the only thing that matters, God’s Will.
Nothing to fear from Satan for a soul in a state of grace. Nuisances and persecutions sign of doing God’s Will. Childish pranks to spiritual giants St. John Vianney.
 Catechism of the Catholic Church 2nd edition #329-331
 https://www.catholiceducation.org/en/culture/catholic-contributions/the-devil-the-fallen-angel.html accessed September 9, 2020
 Ibid 305