Let me repost my comment. Lucifer found in himself an evil desire to destroy.
But there were two countervailing forces: from his nature which had what Hume called “natural sentiment” and from God’s grace or the Holy Spirit’s influence toward the good.
Lucifer weighed these contrary and conflicting desires in his heart and chose the path of evil. Other angels faced a similar choice but chose differently.
What this means is that Lucifer’s heart, his will — that which weighs and chooses in a rational being — was corrupt from the beginning. Which raises the question why God created him like this.
Now in creating the universe, God filled it with life. There is a vast variety of life forms on earth and heaven, writhing and eating each other, from ants to angels. So, there are no “gaps” in which a species would fit but is absent in the creation.
But not so fast. One remarkable aspect of all earthly creatures is that they ascend. Restricting now our attention to humans, they seek their own true happiness and are, as one, directed toward good. They start out as mere single-cell organisms. They grow. They strive. They improve. They end up in heaven in the end.
If all life forms behaved this way, however, then there would definitely be a gap in the universe: things that on the contrary descended would be absent. Enter Lucifer, a being essentially corrupt, a murderer from the beginning.
This understanding neatly solves the apparent scandal of why God’s best creature fell. The reason is obvious: if you want to descend, you may as well start from the very top.
Thus, humans ascend, good angels stay put, and demons descend. The universe is thereby complete. So symmetrical and pretty.
At this point, I am undecided whether Lucifer is a contemptuous jerk or a hateful monster.