a. There are two faculties that constitute our life. One is called the will, the other the intellect. They are distinct from each other, yet they were created to be one. When they are one, they are called “the mind.” Therefore they are the human mind, where all of our life has its first beginning, from which life then comes into our body.
b. Just as everything in the universe–everything that is in the divine design–relates to goodness and truth, so everything in us relates to our will and our intellect. Goodness in us belongs to our will and truth in us belongs to our intellect. In fact, these two faculties or “lives” within us are vessels and abodes for goodness and truth. Our will is the vessel and abode for all things related to goodness, and our intellect is the vessel and abode for all things related to truth. Forms of good and truth exist nowhere else inside us. And since forms of good and truth exist nowhere else, love and faith do not exist anywhere else either, since love relates to goodness and goodness relates to love, and faith relates to truth and truth relates to faith.
c. The will and the intellect also constitute our spirit. That is where our wisdom and intelligence, our love and goodwill, and our life in general reside. The body is merely an obedient servant.
d. Nothing is more important to know than how the will and the intellect become a single mind. They become a single mind the way goodness and truth become one. The marriage between the will and the intellect is in fact similar to the marriage between goodness and truth. As will be shown in the next passage, which concerns goodness and truth, the nature of this marriage is that goodness is the underlying reality of a thing and truth is the resulting manifestation of the thing. Therefore in us our will is the underlying reality of our life and our intellect is the resulting manifestation of our life, because the goodness in our will takes shape and presents itself to be in our intellect.
from True Christianity, Section 387