Some basic Christian truths
Angels as well as humans are created as free beings having the choice between good and evil. Angels are spiritual creatures, while humans are both spiritual and carnal creatures. Satan is an angel, and although he was created by God, he determined himself against God and became evil because of that. The Catechism of the Catholic Church gives us the following explanation:
391 ... Scripture and the Church's Tradition see in this being a fallen angel, called "Satan" or the "devil". 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."
392 Scripture speaks of a sin of these angels. 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." The devil "has sinned from the beginning"; he is "a liar and the father of lies".
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."
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. "The reason the Son of God appeared was to destroy the works of the devil." 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."
422 'But when the time had fully come, God sent forth his Son, born of a woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons.' This is 'the gospel of Jesus Christ, the Son of God':' God has visited his people. He has fulfilled the promise he made to Abraham and his descendants. He acted far beyond all expectation - he has sent his own 'beloved Son'.
423 We believe and confess that Jesus of Nazareth, born a Jew of a daughter of Israel at Bethlehem at the time of King Herod the Great and the emperor Caesar Augustus, a carpenter by trade, who died crucified in Jerusalem under the procurator Pontius Pilate during the reign of the emperor Tiberius, is the eternal Son of God made man. He 'came from God', 'descended from heaven', and 'came in the flesh'. For 'the Word became flesh and dwelt among us, full of grace and truth; we have beheld his glory, glory as of the only Son from the Father. . . And from his fullness have we all received, grace upon grace.'
Satan and other demons are full of lies and with their inspirations they are deceiving people and trying to lead them to sin, or rebellion against God. God loves a man because he created us out of love. God always gives a man a chance to change his life for the better and live in God’s mercy, even after he has sinned. This forgiveness of sins is given to us by Jesus Christ, the Son of God who died for us on the cross. His death redeemed our sins.
Jesus Christ is the winner of the whole human history, as it is written in the Holy Scripture. All those who believe in Jesus Christ are already winners, because they will live together with him in his Kingdom. But this decision has to be renewed in life, because a man is week by his nature and has a tendency to sin. That is why we need prayer and sacramental life, as well as good deeds. God doesn’t demand too much from a man, and his probations are not greater then a human strength. The Holy Scripture tells us about the overwhelming mercy of God, in the way that he forgives sins of a public sinner, the adulteress and of the repenting criminal. But these people accept God’s forgiveness and change their lives. The criminal on the right, being aware of his sins, humbly prays: "Jesus, remember me when you come into your kingdom." Jesus answered him, "I tell you the truth, today you will be with me in paradise." (Luke 23, 42). I think that these are the most beautiful words in the whole Bible.