Owen Barfield typically explained himself by starting with evidence (for example the evidence for evolution of language, or for understanding human evolution as beginning with consciousness) and leading up to his conclusions.
However, I suspect it may be easier to understand Barfield if we begin with his conclusions, and then describe how these conclusions can be used to interpret the evidence.
This may be easier to understand; and it is also more correct - because evidence is always capable of multiple interpretations and therefore many people will get 'stuck' in the evidential stage of Barfield's arguments and never arrive at the point of understanding where the arguments were leading, or why.
For example, Barfield vastly documented the evidence for the evolution of meanings of words, and interpreted this as evidence of changing human consciousness. However, the fact is that there are other, especially cultural, ways of explaining the pattern of changes in meanings of words without invoking an evolution of human consciousness. (Indeed, Barfield's ideas are quite often misinterpreted as being a type of 'pot-modern' cultural relativism.) The same applies to all other sources of evidence.
As so often, it is a matter of metaphysical assumptions. Normal mainstream modern people have (largely unconscious and unacknowledged) assumptions such as that bodies evolved before minds, and that minds evolved before consciousness; and that human consciousness is the same in all cultures and at all points in history. All evidence is interpreted in light of these assumptions - and therefore evidence cannot challenge these assumptions.
Therefore it may be helpful to start with the destination; to start with Barfield's assumptions. For example that There is a God, Christianity is true, God has a plan for the evolution of human consciousness, that this plan aims at making Men into Gods, and that the whole of creation is organised around this.
But the divine destiny entails Men becoming more and more free, as their selves become more distinct from the rest of creation - so that, individually or collectively, Men can and do refuse to go-along-with God's hopes and plans for our evolution.
Once this is understood, it may be easier to grasp what Barfield is saying.