Nature of devotion is such that you feel longing in its absence. Once you get a glimpse of devotion then its absence causes perturbation in mind. it is not that devotion is absent but you feel as if it is not there.. the very indication of devotion is that you experience bliss in its presence and its absence makes you restless.
As used in language study, and very briefly defined: communication is a successful act of information transfer, while conversation is an informal social activity.