What remain constant in every account of angels, from ancient days to the present, is that they are both messengers and companions to humans, sent from a realm beyond usual seeing. Angels appear, and in one way or another, help us, advise us, inspire us, or amaze us.
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.