Thus, Rahner introduces "transcendental Christology", which interprets the event and person of Christ in relation to the essential structure of the human person, reflecting on the essential conditions of all human experiences, conditions which transcend any one particular kind of experience. One should however first look into Rahner's basic insights on Christology within an evolutionary view of the world, which claims that Christian faith sees all things in the world come from the one same origin, God. This means that in spite of their differences, there is "an inner similarity and commonality" among things, which forms a single world. This commonality is most clearly disclosed in a human being as a form of the unity of spirit and matter: it is only in a human person that spirit and matter can be experienced in their real essence and in their unity. Rahner states that "spirit" represents the unique mode of existence of a single person when that person becomes self-conscious and is always oriented towards the incomprehensible Mystery called God. However, it is only in the free acceptance by the subject of this mystery and in its unpredictable disposal of the subject that the person can genuinely undertake this process of returning to the self. Conversely, "matter" is the condition which makes human beings estranged from themselves towards other objects in the world and makes possible an immediate intercommunication with other spiritual creatures in time and space. Even if there is an essential difference between spirit and matter, that is not understood as an essential opposition: the relationship between the two can be said as "the intrinsic nature of matter to develop towards spirit". This kind of becoming from matter to spirit can be called "self-transcendence" which "can be only understood as taking place by the power of the absolute fullness of being": the evolutionary view of the world allows us to consider that humanity is nothing but the latest stage of the self-transcendence of matter.