It's our proceeding power, according to Charles Fillmore. It's how we can look beyond the physical into the spiritual. It's how we can know from within that we're the child of God. That perception takes place in our brain, so Faith correlates with our brain. Love, as you can well guess, relates to the heart and to the circulatory system, anything to do with the circulation of the blood.
Strength correlates with our spinal cord and our nerves, our backbone.
We talk about people who are strong and steady as having lots of backbone. Those who are weak and lifeless and who have ambivalence are called spineless. Our language gives us clues to all of these powers. We all have an inner awareness of this. The next power is called Wisdom and Good Judgment, and it relates to the pituitary gland or master gland.