Or to express the same thing again, in another shape, the great business of the creature is, not to be without action, but to act in concurrence with God, to harmonize with God. This was the prayer of the Savior, “as thou, Father, art in me, and I in thee; that they also may be one in us.” To express the whole as simply and briefly as possible, the sum of religion is unity with God. And this unity, which cannot exist without the concurrence of the creature, is secured by faith. It is not possible for God to be in union with any being, that has not confidence in him. A want of confidence, which is the same thing as a want of faith, is itself disunion.
— edited from The Life of Faith (1852) Part 1, Chapter 7.