As for the earthly self being split into two levels, this is an actual division of both will and thought. Every action that we take originates in our will; every word we say originates in our thought. Below our first earthly will, we ourselves create a second will and a second thought process, which also belong to our earthly self. The will that we create ourselves could be called our bodily will, because it drives the body to behave in moral ways. The thought process that we create ourselves could be called lung-related thought, because it drives our lips and tongue to say things that show a good understanding.
Taken together, this type of thought and this will can be compared to the inner bark that adheres to the outer bark of a tree; or it can be compared to the membrane that adheres to the shell of an egg. Behind this self-made thought and will lies the inner earthly self. If we are evil, our inner earthly self is like rotten heartwood within a tree whose outer and inner bark appears whole; or like a rotten egg inside a clean white shell.
Now to the nature of the inner earthly self that we are born with. Its will has a tendency toward evils of every kind and therefore its thinking has a tendency toward falsities of every kind. This inner self, then, is what needs to be regenerated. If it is not regenerated, it harbors hatred toward everything related to goodwill and anger at everything related to faith.
It follows, then, that our inner earthly self must be regenerated first, and our outer self must then be regenerated through our inner self. This sequence follows the divine design. To regenerate our inner self through our outer self would go contrary to the divine design, because the inner self acts as the soul of the outer self, not only in a general way but in every detail. The inner self is present in everything we say, without our even realizing it. This is what allows angels to perceive the quality of our will from a single action of ours, and the quality of our thinking from a single thing we say—the “quality” meaning whether we are hellish or heavenly. As a result, they have complete knowledge of us. From our tone of voice they perceive the interests that drive our thinking; from a gesture of ours, or the form of one action, they perceive the love that resides in our will. They detect this no matter how good we are at presenting ourselves as a Christian and a moral citizen.
from True Christianity, Section 593