Ellen White wrote the following about Satan's repentance in Spirit of Prophecy, vol. 1 (1870):

Satan trembled as he viewed his work. He was alone in meditation upon the past, the present, and his future plans. His mighty frame shook as with a tempest. An angel from Heaven was passing. He called him, and entreated an interview with Christ. This was granted him. He then related to the Son of God that he repented of his rebellion, and wished again the favor of God. He was willing to take the place God had previously assigned him, and be under his wise command. Christ wept at Satan's woe, but told him, as the mind of God, that he could never be received into Heaven. Heaven must not be placed in jeopardy. All Heaven would be marred should he be received back; for sin and rebellion originated with him. The seeds of rebellion were still within him. He had, in his rebellion, no occasion for his course, and he had not only hopelessly ruined himself, but the host of angels also, who would then have been happy in Heaven had he remained steadfast. The law of God could condemn, but could not pardon. {1SP 29.2}


He repented not of his rebellion because he saw the goodness of God which he had abused. It was not possible that his love for God had so increased since his fall that it would lead to cheerful submission and happy obedience to his law which had been despised. The wretchedness he realized in losing the sweet light of Heaven, and the sense of guilt which forced itself upon him, and the disappointment he experienced himself in not finding his expectations realized, were the cause of his grief. To be commander out of Heaven, was vastly different from being thus honored in Heaven. The loss he had sustained of all the privileges of Heaven seemed too much to be borne. He wished to regain these. {1SP 30.1}


This great change of position had not increased his love for God, nor for his wise and just law. When Satan became fully convinced that there was no possibility of his being re-instated in the favor of God, he manifested his malice with increased hatred and fiery vehemence. {1SP 30.2}


God knew that such determined rebellion would not remain inactive. Satan would invent means to annoy the heavenly angels, and show contempt for his authority. As he could not gain admission within the gates of Heaven, he would wait just at the entrance, to taunt the angels and seek contention with them as they went in and out. He would seek to destroy the happiness of Adam and Eve. He would endeavor to incite them to rebellion, knowing that this would cause grief in Heaven. {1SP 30.3}