The supernatural creaters put a lot more thought into Supernatural then anyone thinks.
Sam, who posseses supernatural powers and whom the demons believed would lead them is actually another name for Samael.
Hebrew beliefes state that Samael is an archangel, a figure who is accuser, seducer and destroyer, and has been regarded as both good and evil.
Also called Sammael and Samil (and is even sometimes confused with Satan) he is considered in legend both a member of the heavenly host (with often grim and destructive duties) and a fallen angel, equatable with Satan and the chief of the evil spirits. One of Samael's greatest roles in Jewish lore is that of the Angel of Death. In this capacity he is a fell angel but nevertheless remains one of the Lord's servants.
Beliefs describe Samael as a "Power", being the chief of many warrior angels:
Powers are Warrior Angels against evil defending the cosmos and humans. They are known as potentates. They fight against evil spirits who attempt to wreak chaos through human beings. The chief is said to be either Samael or Camael, both angels of darkness.
Lilith is said to be Eve, the first women. It was she who left Adam and left to marry Samael. (Adam from the story of Adam and Eve).
Now Lucifer was once known as Samael and in some religions was believed to be an Archangel turned bad.
I believe that these facts may be partially correct and that they are part of supernatural because of how the angel called Sam "Samael" in one of the episodes.
Ok, now my theory is that lucifer is trapped inside Sam and that Lilith (whom is in love with Lucifer) wishes to free him from Sams body. This is why she is breaking all the seals.
I think this is why the angels don't like Sam and they do not want him to use his powers for fear that it may awaken what is inside him.