Like I said: I'm an archangel, one of four brothers that predates the other angels and all of mankind. God created the Earth and all of its living creatures. He made humans, and he loved them most of all.
He loved them so much, in fact, that he thought that angels ought to be subservient to them — including us, his first children, his trusted soldiers. I loved my father more than anything, I couldn't stand to not be the favorite in his eyes. I refused to kneel to his new playthings, and I was banished. Thrown out.
I was cast down into Hell and locked away in a Cage for millions of years, only to be let out when it was prophesied that I would battle my brother Michael for the Earth. We were destined to have vessels for the coming fight — Michael was given Dean Winchester. I was given Sam Winchester.
The Winchesters had other plans. They thwarted the Apocalypse, they locked me and Michael back in the Cage, they shattered God's plan and threw the world into chaos in the name of saving humanity — but in the process created power vacuums in both Heaven and Hell that led to uprisings and unbelievable carnage, which they don't care about because they're human. Not that humans are much safer, because the Winchesters and Castiel unleashed not only the Leviathans upon the world, but also caused the angels to all be cast out of Heaven (and they did not like that). They stumbled on without a plan or any knowledge of how the world works and unleashed the Darkness, a primordial force far beyond their realm of understanding that's been locked away since my time in Heaven.
They came to me for help. They don't have the power or knowledge to fight her.