Human reasoning is not enough: there will always remain an "irrational residue" which escapes analysis and which can not be expressed in concepts: it is this unknowable depth of things, that which constitutes their true, indefinable essence that also reflects the origin of things in God. In Eastern Christianity it is by faith or intuitive truth that this component of an objects existence is grasped.[71] Though God through his energies draws us to him, his essence remains inaccessible.[71] The operation of faith being the means of free will by which mankind faces the future or unknown, these noetic operations contained in the concept of insight or noesis.[72] Faith (pistis) is therefore sometimes used interchangeably with noesis in Eastern Christianity.