Lucifer and a third of the angels disobeyed God.
They did more than just that. Lucifer wanted to be God. We see this in the temptations of Christ. Lucifer wanted Christ to worship him.
Lucifer will do any and all things to keep the attention away from Christ and His work on the cross and His coming glory.
Lucifer wants us to get all tangled up in rules and regulations and works to justify our salvation. He knows if we start thinking, "look what I've done, look how good I've been", we slowly take our eyes of Christ and put them on our own filthy works. Slowly, over time, you've forgotten about Christ and you're thinking about yourself.