Soul Channeling

Soul Chaneling is the ability to channel a soul to power a spell or another power. It is highly dangerous and easy to destroy the soul and kill the person. Known things with this ability are:

Angels - Angels may channel souls for power, demonstrated by Castiel, most notably with the souls of Purgatory.

Archangels - As they are more powerful than normal Angels, it is presumed they possess this ability.

Humans - Henry Winchester, a Man of Letters, was able to channel his soul to power a time-traveling spelll.