The two biggest mirrors for Dean in Stairway to Heaven were two angels, both of them in female vessels. The first was Flagstaff, as she liked to be called, who prided herself on helping people at the hospital by performing minor miracles. When Dean tells her he is also in the business of saving people she laughs, saying:
But you, thinking you help people. It’s amusing. I help people. Clogged artery here, tumor there. I do good in this world. You, you believe every problem can be solved with a gun. You play the hero but underneath the hype you’re a killer, with oceans of blood on his hands. I hate men like you.
She is a mirror for what Dean wants to be, someone who does more good than harm, but she’s spitting his own worst fears right in his face. He always tries to believe that he’s doing the right thing, but he’s saving people less and less, and is succumbing to the effects of the mark more and more. He truly believes he is a killer, that he is what the blade is stirring up inside of him. This is why he lashed out in such anger. She told him exactly what he said to Sam on that bridge in Road Trip. That he is poison.
Then we have Tessa, an angel of death whose sole purpose for existing is ushering souls off to the afterlife. But Heaven is boarded up, and she can’t do her job. She can’t save people, so what good does her existence do? She is who Dean believes he is. A desperate, wounded animal crying out for help, too afraid to just end it all because they both feel their deaths need to have purpose and serve some greater good.
Two mirrors, one who does good but tells him he does not. One lost, who wants to help but is utterly incapable of doing so. How ironic that Tessa would end up in chains, like Gadreel, and like Dean is in so many ways on the inside. Chained to her duty, utterly paralyzed and lost due to her inability to perform what she believes to be her only reason for existing.