What is Sin ?

The Origin of Sin: First of all, Sin is the transgression of the law (of God). If there is no sin, then there is no law and vice versa. The first sins in heaven were pride, jealousy, envy, rebellion...none of which existed in heaven until Satan wanted Jesus' place in heaven.
In the last book of the Bible, Revelation 7-10, we read that there was a war in heaven and it continues on earth. The war was/is between good and evil. Humanity has the freedom from God to choose whom to worship; God or Satan. Deuteronomy 30:15-16If a thing is free to be good, it's also free to be bad." -C.S. Lewis
Free will (freedom) is what has made evil possible. Why, then, did God give humans free will? Because free will, though it makes evil possible, is also the only thing that makes possible any love or goodness or joy worth having. The beautiful, exalted angel, called "son of the morning", who also had free will, became lost on an ego trip. He coveted the glory and homage due to God alone. He was power hungry and had the boldness to challenge his Creator for the rulership of the universe.
Faith can provide strength and comfort during difficult times. It can help people find hope and meaning in their struggles, and give them the courage to keep moving forward.