MORE ABOUT LUCIFER:
Lucifer was one of only four angels who knew the face of God. He was said to have loved God more than any of the others. Those two things are central to who he is, as much as his pride and hatred are. When one thinks of Satan they think of brimstone and pitchforks. In Supernatural, Lucifer is all of Sin but he’s also an angel, and he always will be.
Angels aren't like humans. They're dispassionate soldiers, and they intervene on earth out of duty rather than out of any sense of love or compassion. This is in large part because of Lucifer. Prior to the creation of the humans, angels were a lot like we are; they had emotions and desires.
When mankind was born, God asked the angels to lay that aside and love and protect us even more than they loved Him. Lucifer refused to the point of rebelling and starting a civil war. This indicates two things about him:
1) he is fiercely loyal;
2) he never backs down when he thinks he is right, no matter how much he loves whomever opposes him.
"Loyalty" to him means he will always love you but if he's right and you're wrong, get out of his way.
After the war in heaven, Lucifer was banished but he got to keep his emotions. The angels in heaven were “reprogrammed”, presumably out of fear that Lucifer had corrupted them. Even after the civil war, Lucifer desperately wants the other angels to join him. He loves his brothers and sisters…some more than others. Like God, Lucifer plays favorites. When Castiel banished Michael with Holy Fire, Lucifer killed his younger brother without so much as a flicker of remorse.
However, when Lucifer was faced with the archangel Gabriel-another younger brother, but one he loved much more deeply-he begged Gabriel not to “make him” kill him. But Lucifer still did. As noted, he never gives up on his goals. That doesn’t mean he won’t have some remorse; after killing Gabriel, Lucifer stands alone over his body and is brought to tears.
He is also remarkably honorable. The trait he most adheres to is loyalty. He compliments Castiel on it when the younger angel lies to protect the Winchesters, and he chastises Gabriel over his lack of it ("you disloyal--").
Furthermore, Lucifer is always up front and honest. As he puts it, he doesn’t need to lie; the truth is on his side. It’s also true, however, that he doesn’t need to lie because he doesn’t fear anyone. Even God is the subject of Lucifer’s wrath, though he phrases it more gently: he wants to “find Him” and “hold Him accountable for His actions”. Everything Lucifer does is in pursuit of that goal.
Although he has respect for those he considers family that doesn’t mean he sees them as equals. That’s something all the archangels seem to share: they do not tolerate people mouthing off to them. Zachariah threatens Sam’s life when Dean is smart with him; Gabriel repeatedly tries to put the Winchesters in their place (first as a trickster and then after they learn who he really is). And although Lucifer loves the other angels, but he tells Gabriel to “watch his tone” when he is getting out of line.
This all indicates they have pretty high levels of self-respect and egos to match, which reflects on Lucifer’s legendary pride. It’s important to note this because you shouldn’t mistake his sorrow for self-loathing. He doesn’t hate himself, he hates everyone else for forcing him to do things he doesn’t enjoy doing. This is in spite of the fact that, as Gabriel points out, “no one makes [angels] do anything”. All the angels have some degree of immaturity, and that is Lucifer’s.
Another popularized facet of Lucifer’s personality is his temper. It isn’t as close to the surface as you might think. In fact, Lucifer is incredibly patient. When Gabriel deliberately pushes his buttons, Lucifer simply warns him to back off. He also allowed Sam to do or say nearly anything he wanted, at every one of their meetings. Some of that courtesy even extended to Dean; after being shot in the head with the Colt, Lucifer doesn’t kill Dean, he simply knocks him aside and continues on with his work. Undoubtedly he was lenient because he needed Sam, but it still shows that he actually has his temper very well in hand.
Of course, Lucifer is not a pacifist. There are a few times throughout the season where his calm demeanor and patience are mistaken for loyalty. He has indescribable amounts of disgust for the human race, but it’s even worse for pagan deities. In Hand of the Gods, Lucifer is summoned by one of the pagans. Instead of gratitude, he expresses his distaste for them and proceeds to kill them off one by one, to the dismay of the deity that had summoned him.
The demons have the same dilemma. They see him as their Father, and he sees them as fodder. However, at one point Meg interacts with Lucifer one on one and he is seen caressing her face and smiling before he leaves. Lucifer claims he doesn’t use tricks, and he doesn’t lie, but that may mean he doesn’t lie to humans. It may also mean that he does have some affection for certain demons.
Lucifer is clearly powerful and charismatic enough to sway those who should know better. When he rebelled, one-third of the Heavenly Host is said to have followed him even into hell, and the pagan messenger obviously had no idea Lucifer would turn on him. The Four Horsemen as semi-autonomous, especially Death, and yet Lucifer was able to get them to work for him. The demon Crowley knows that Lucifer will destroy Hell and all the creatures in it, and yet he can’t convince the demons to be disloyal to Lucifer.
Perhaps a part of that is an aspect of his personality that is only hinted at: a sense of humor. The biggest indication of it is in his fight with Gabriel, when he says, "Don't forget: you learned all your tricks from me." Gabriel is of course also known as The Trickster. There are smaller signs as well: when Lucifer rings the bell for service at the hotel, when he draws a pitchfork on a frosted over window, and the way he sometimes sing-songs his words or peppers his speech with pop culture and Biblical references.
The only sure thing about Lucifer is that he wants everything but the loyal angels dead. Every insect and bird and man and woman and child. When he's done with earth, he's going to destroy Hell.
In the meantime, don't worry. He can promise you that everything you're doing is part of the plan.