There was a time when Satan was in harmony with God, and it was his joy to execute the divine commands. His heart was filled with love and joy in serving his Creator, until he began to think that his wisdom was not derived from God, but was inherent in himself, and that he was as worthy as was God to receive honor and power.—The Signs of the Times, September 18, 1893. TA 31.3
Though God had created Lucifer noble and beautiful, and had exalted him to high honor among the angelic host, yet He had not placed him beyond the possibility of evil. It was in Satan's power, did he choose to do so, to pervert these gifts. He might have remained in favor with God, beloved and honored by all the angelic throng, presiding in his exalted position with generous, unselfish care, exercising his noble powers to bless others and to glorify his Maker. But, little by little, he began to seek his own honor, and to employ his powers to attract attention and win praise to himself. He also gradually led the angels over whom he ruled to do him service, instead of devoting all their powers to the service of their Creator.—The Spirit of Prophecy 4:317. TA 31.4
Little by little, Lucifer came to indulge the desire for self-exaltation.... Though all his glory was from God, this mighty angel came to regard it as pertaining to himself.—Patriarchs and Prophets, 35. TA 32.1