He can tell that Dean sees Death as an enemy. Quite understandable, as Death had snatched his mother, father, brother, and other loved ones from him in times passed. Dean sees Death as something to be hated. A cruel hand that controls the reaping scythe, cutting down old and young, weak and strong, worthy and unworthy, deserving and not. Uncaring of the victim, wishing only to take his fill of the humans that roam the realm. It shows on his face when he looks at a lifeless body during a case, a soul-deep hatred that burns hotter than the pits of hell and twice as tortuous. Death cannot be brought to justice for his sins. Death cannot be harmed or killed. Death is untouched, a very part of life itself, entwined with the very fabric of the universe. There is no life without Death and no Death without life. Dean clearly resents him for that.
He, however, doesn't.
Death has taken his brothers and sisters before, and Death will take more. Death will take his Father and the Enemy. Death will take him. Death will take the Winchesters. Death will take the very universe and will perhaps then take itself. He cannot resent him for that, not when it is his purpose. Death is not an enemy, he thinks, but a friend.
He can see a grizzled old woman, her life filled with pain and hardships and strife, and finally, blessedly, Death takes her. She isn't grizzled and pained then. She is pure. Whole. No longer old and scarred, but young and new, innocent and unblemished. Released from the darkness of a life that tears at and destroys the pure and the innocent, twists and burns them until they melt and are maleable, its gnarled fingers knotting and breaking and pulling and shaping until innocence is lost and broken, and a new unholy creature arises. But Death takes her hand and the unholy creature cracks open and reveals the innocence, complete and raw and pure once more. Death greeted her as friend and stole her away from the world and her suffering.
He can see a young child, sick and pained, unable to move as the sickness wears away at its exhausted, frail body. The only hope for the babe is that its body will not build an immunity to the painkillers. Death comes and is merciful, recognising that the child will know only agony. No happiness, no laughter, nothing but screams when the medication fades and tears when nothing takes it away. Death embraces the child and ferries it to a better shore, one where no sickness nor pain is allowed. The disease is gone and the child runs through the fields of its heaven.
It is a great, overwhelming sadness when Death takes a loved one. However, Death does not come vengefully. Death does not come in rage, devouring those whom he wishes to, causing misery and suffering. Death comes gently and ushers the dying off into a better land.
Dean sees and enemy, while he sees a friend. He supposes it is merely the difference between the mind of a mortal and that of a celestial being. Perhaps it is because he has seen far more lives taken by Death. Perhaps he understands. And perhaps he will welcome the cool arms of his friend one day. However, not today. Today, he is needed. Death will wait.