Lucifer is not "redeemable". He is completely right from his own point of view. I suggest you read Arthur Milton's "Paradise Lost" (with illustrations by Gustave Dore!) and find out his story in the old testament.
Basically he was the favorite child of god, one of the archangels, and when god announced his plans to create some losers made of flesh and put them in "garden of eden" and that all angels must bow before them, he rebelled, so did about 30% of ALL ANGELS with him. There was a war, and they lost and were banished to some place else.
Later he heard about this "man" and flew through planes and changed his appearance to another angel to enter the garden of eden and check them out. They were to naked humans just chilling and enjoying life. He saw what a wonderful place God created for them and was a bit jealous. But he escaped before other angels caught him. But he entered their dreams and made them ashamed that they were naked, so Adam and Eve began wearing fig leaves over their genitals. God was furious that they werent pure anymore so he scolded them.
So he went back and told the angels following him about all this, and they built an army and started a new war, I think God sent Jesus and he was too powerful for Lucifer's angels and they lost.
In the meanwhile Lucifer was allowed into the garden of eden again , he changed into a snake and entered Eve's dream and told her that they could eat from the tree of knowledge and know about all. She woke up and convinced Adam to join him. They ate and learned about everything. Think of it as the main computer of heavens with google and shit.
So god and Archangels knew of this immediately and and decided human cant stay in the garden of eden anymore. Lucifer met them once and already corrupted them. And they were cast on Earth, and told of all their future (their children killing eachother etc etc doomsday etc) and that they will be allowed back into the garden of eden (or paradise) again in the future.
This paradise is NOT HEAVEN. Where angels live, where god lives IS NOT the same as Paradise (or Garden of Eden) It's made for humans and it looks like Earth, with perfect climate, land etc. So when you go, you don't go to heaven, you go to paradise. Makes sense?
Now Lucifer is the one that taught humanity not to obey blindly to their superior, and instead search for the truth and learn. So he gets vilified.
That's why he is so pissed at god. First he creates lesser beings and loves them over his most beloved children. Then asks his children to bow before these beings, which are flawed. And punishes them when they don't. Even when they prove that human is easily corrupted and weak.
From Lucifer's point of view: he is not evil. God is, humans are, but not him. Would you also not be pissed if your parents made a new kid, told you to give all your toys to him, eventhough he's this idiot kid that tortures the family dog, kills bugs etc, then they kick you out for not going with this anymore: and you are evil.
Lucifer in the new season is nothing like the biblical lucifer, and he is nothing like when Lucifer first appeared in the series. They screwed up. The writers probably havent even read the bible or any reference text about lucifer before writing for the new season. "Ok lucifer bad guy? yes I can write that episode. easy. I've heard a lot about lucifer. He is literally donald trump!"
Supernatural is mainly based on biblical mythology in its story writing. But they fucked it up on the last season