Complex sentence: The Bab wrote: "He Who will shine resplendent in the Day of Resurrection is the inner reality enshrined in the Point of the Bayan" that Bahais believe referred to Baha'u'llah being the inner reality of The Bab.
Split into simpler sentences: The Bab wrote: "He Who will shine resplendent in the Day of Resurrection is the inner reality enshrined in the Point of the Bayan". This is that which Bahais believe referred to Baha'u'llah being the inner reality of The Bab.