The term "heart" (qalb/fu'ad) appears throughout Bahá'u'lláh's writings with seemingly different valences depending on the context. In the earlier Arabic writings — particularly the Hidden Words and some of the tablets composed during the Baghdad period — the "heart" seems to be understood in a strongly Sufi-inflected sense: the innermost seat of mystical perception, the locus of divine emanation, the mirror that must be polished. This resonates closely with Ibn 'Arabí's concept of the qalb as the faculty that "turns" (from the root qalaba) to receive divine self-disclosure.
But in some of the later Persian and Arabic tablets — particularly material from the Akká period — the usage seems to shift toward something more broadly devotional or moral: the heart as the seat of intention, sincerity, and ethical commitment. Is this a genuine doctrinal shift, or is it a difference in rhetorical register? I'm curious whether anyone has done systematic work tracking this across the corpus, or whether there's secondary literature in the Irfán papers addressing it.