5 - Accessing Earlier Stages
It is vital to appreciate that this integration cannot be successfully achieved at an earlier stage.
A degree of integration - that is appropriate to the nature of the stage in question - must indeed take place at all levels of development.
However as the first task of development relates to successful differentiation, this aspect dominates through the earlier stages. Thus the integration that takes place is in the context of enabling an increasingly more differentiated worldview.
As we have seen this culminates with the stages of the middle level (which represents the specialisation of this differentiated worldview).
So for example the integration of body and mind of the centaur (the most advanced of the middle stages) - relative to that of full spiritual integration - is of a very reduced nature. It mainly enables the ego-based personality to perform in a creative and productive manner (within the context of the worldview defined by the centaur).
The true process of spiritual integration really starts with the first of the "higher" levels (H1).
By its very nature such integration requires bringing to light for the first time (prepersonal) elements that are necessarily repressed (during the early development of L1).
These elements cannot be integrated at an earlier stage as the quality of spiritual light (that is necessary to access them) is not available at that time.
So the return to earlier levels is not just due to earlier unscheduled problems with development (though this of course can also be a factor). Even when development goes fully right - insofar as this is possible - the return to the earlier levels is vital. This is especially so the deeper the nature of spiritual development that is involved. Indeed even the view that it is a return to "earlier" levels is somewhat linear as ultimately "higher" and "lower" are seen as fully interdependent.
So as Underhill portrays so well, progression (under the spiritual guise of illumination) is inevitably followed by regression (under the spiritual guise of purgative darkness).