Here is Zosima’s advice to Madame Khokhlakova in Dostoevsky’s The Brothers Karamazov concerning how to achieve certainty in her religious faith through the experience of active love:
Strive to love your neighbors actively and tirelessly. To the extent that you succeed in loving you will become convinced both of the existence of God and the immortality of your soul. If you attain complete selflessness in loving your neighbor, then you will indubitably be persuaded, and no doubt will even be able to enter your soul. This has been tested, this is certain.
In Dostoevsky the Thinker, James Scanlan writes:
The connection between love and faith as Zosima expresses it, making love a sufficient condition for the consolidation of faith, is somewhat puzzling. Why, psychologically, should loving other human beings make us more disposed to believe in God? Dostoevsky does not explain the connection in so many words, but in the light of his notes for “Socialism and Christianity” we can conjecture that he identified the need for faith as a need for connectedness, for the completion lost with the individualization of society, and that he saw love as constituting precisely such selflessness – as giving oneself to others, preferring others over oneself. In this sense, to love is to place oneself within the eternal, spiritual “higher synthesis” of being that constitutes what I have called Dostoevsky’s philosophical conception of the deity.