Board Thread:Warhammer 40k General Discussion/@comment-6078851-20130318203252/@comment-3258762-20130402181733

Well, the thing is, the Imperial Truth was a lie. It was meant to starve the Chaos Gods, but since the Chaos Gods do not feed on worship, or at least not to survive, but emotion, it failed. Then, the Emperor realised in his last moments before being interred in the Golden Throne, that religion was the key, and that by worshiping him, then he could become powerful enough to fight the Chaos Gods, and he is, he is fighting them every day in the Warp, during the Age of Apostasy, the Warp Storms were because the Chaos Gods were starting to overpower the Emperor, which then failed because he beat them back.

He realized this because he finally got an understanding of why the people needed religion, something he could never understand before because he had never been faced with anything he could not explain, but when Malcador gave him his life-force, he saw the universe from the eyes of a mortal man.

So I believe fully that the Emperor is giving power to the Saints and the Sisters of Battle, and the reason Euphrati managed to wield her faith as a weapon was because, to the Chaos Gods, the Emperor is like a Pariah would be to a Psyker. The Daemon felt that she was drawing power from her emotions for the Emperor and her hope in the Emperor and it couldn't take the strain of the greatest weapon of all: The Mind.