This is one of the things that love is called upon to do:
To affirm and sustain the seed in another human being even though no tangible evidence has been given of the nature and quality of the seed that is growing there. Love depends upon the capacity to reach beneath the surface of persons, to feel and touch the seed of life that is hidden there. And love becomes a power when it is capable of evoking that seed and drawing it forth from its hiding place.
The smile of the contemplative in the presence of the Beloved is merely a physical expression of the total joy one perceives as one communes with God. St. Bernard used to say, "The joy of being in love is in the very loving." In other words, joy is not to be sought for itself, but is a by-product of love, and the smile is but the physical, exterior expression of the inner joy-love.