Complex sentence: The concept of "oceanic feeling" was coined by Romain Rolland in his Correspondence with Freud, based on his studies of Eastern mysticism, in which correspondence he wished to hear Freud's analysis of the concept, which was answered in these books.
Split into simpler sentences: The concept of "oceanic feeling" was coined by Romain Rolland in his Correspondence with Freud, based on his studies of Eastern mysticism. In the correspondence, Rolland expressed a wish to hear Freud's analysis of the concept, which he answered in these books.