Board Thread:Warhammer 40k General Discussion/@comment-6767898-20130227013545/@comment-7855563-20130409211230

And we reach the central point of what the Imperium was founded upon: Faith. While the Emperor looked down upon religious faith, he upheld faith in humanity as a point in which to build the Imperium. Logar was right when he said that humans strongest attribute was faith, but he was so blind to the true Imperial Creed. It is faith in the Space Marines, the Primarchs, the Emperor, in the Imperium that drives it.

It is also why the Ultramarines allow normal humans access to Guilliman. Faith that he will return. Faith compounded by seeing the son of the God-Emperor. Faith that they are being protected by the sons of this demi-god held in the throes of death. Faith in the power and righteous fury of the Imperium.