And it is proper to say here, that faith is the source, the parent of all true feeling and affection in the natural sense, as well as in the religious sense. Certain it is, that this statement admits of an easy and a satisfactory illustration in the case of the affection of love. It requires no proof to sustain the assertion, that natural love is based upon natural faith. If we have entire confidence in another, if we believe him to be amiable and pure in feeling, and upright in principle, it is the natural result of such confidence, that we shall love him. And on the other hand, it will be very difficult, and I think we may say, it will be found naturally impossible for a person to love another, (except, perhaps, with that lower form of love, which is synonymous with pity or sympathy,) in whom he has no faith. And the same confidence, the same faith, which inspires the affection of love in the first instance, gives it permanency in time to come. The one perpetuates itself in company with the other. Suggestions may arise, and temptations may assail us, but love will live, if confidence does not perish. But how soon does our love to a person, to whom we were once devotedly attached, cease, when our faith in him ceases! No sooner is the confidence, which we reposed in his amiability, in his truth and honor, and other estimable qualities, taken away; in other words, no sooner is our faith in the existence of these traits taken away, than the love, which rested upon it, falls at once to the ground.
The law of the religious affections is the same. They always imply the antecedent existence of faith. Religious faith, sustained by the Holy Spirit, but operating in a manner entirely analogous to the operations of natural faith, is undoubtedly the true basis of religious love. Without the key of faith the foundation of divine love, which refreshes and gives beauty to the whole soul, would never be opened within us. It would be impossible; because it would obviously be a result, not only without reason, but against reason. It is because we believe or have faith in God as just, benevolent and holy, as possessed of every possible perfection calculated to attract and secure our love, that we love him.
— from The Life of Faith (1852) Part 1, Chapter 6.