That sin by the commandment might become exceeding sinful. Romans 7:13. The Faith I Live By 70.1

In great mercy, according to His divine character, God bore long with Lucifer. The spirit of discontent and disaffection had never before been known in heaven. It was a new element, strange, mysterious, unaccountable. FLB 70.2

Lucifer himself had not at first been acquainted with the real nature of his feelings; for a time he had feared to express the workings and imaginings of his mind; yet he did not dismiss them. He did not see whither he was drifting. But such efforts as infinite love and wisdom only could devise, were made to convince him of his error. His disaffection was proved to be without cause, and he was made to see what would be the result of persisting in revolt. Lucifer was convinced that he was in the wrong.He saw that “the Lord is righteous in all his ways, and holy in all his works” (Psalm 145:17); that the divine statutes are just, and that he ought to acknowledge them as such before all heaven…. He nearly reached the decision to return; but pride forbade him…. He persistently defended his own course, and fully committed himself to the great controversy against his Maker…. FLB 70.3

Satan’s rebellion was to be a lesson to the universe through all coming ages—a perpetual testimony to the nature of sin and its terrible results.The working out of Satan’s rule, its effects upon both men and angels, would show what must be the fruit of setting aside the divine authority. It would testify that with the existence of God’s government is bound up the well-being of all the creatures He has made. Thus the history of this terrible experiment of rebellion was to be a perpetual safeguard to all holy beings, to prevent them from being deceived as to the nature of transgression, to save them from committing sin, and suffering its penalty. FLB 70.4

The infinite value of the sacrifice required for our redemption reveals the fact that sin is a tremendous evil.FLB 70.5