We Have Not The Luxury To Count The Cost
“Know this adept, for your journey has been long and you are to be trusted as few will ever be. Psykers represent Humanity’s future, the ideal creature into which mankind will evolve; a more powerful, more intelligent and more capable life form. As yet this race is weak, its members lacking the mental strength needed to face the dangers of the psychic universe. Were the new race of psykers permitted to develop free and unprotected, the whole of Humanity would soon be destroyed. We few who are privy to this truth have guarded it selflessly for nigh on four millennia, since the end of the great schism from which our order was born. It is our sole concern, for the very future of our race depends upon us, and us alone.” -Transcription of suppressed texts, from the archives of the Gethsemene Reclusium
A Psyker is an individual who possesses some degree of psychic ability or powers. Psychic powers are sometimes referred to as sorcery in the Imperium of Man, particularly when such powers are used in such a way that they show no regard for the dangers they may spawn for others or they are used in pursuit of the agenda of the Chaos Gods. Psykers draw their powers from the dimensional realm known as the Immaterium or the Warp that underlies four-dimensional realspace and is the source of all psychic energy in the universe. As such, psykers, are often in danger of possession by the daemonic entities of the Warp, insanity and ultimate corruption by the Ruinous Powers of Chaos.
Many amongst the Inquisitors and their Acolytes are Pskyers themselves, although these are almost always subjected to intense training, tests, and scrutiny to ensure that they do not fall sway to insanity or chaos.