I'm convinced there's some significance in his choice of church and date. At first I thought of the charitable practice of leaving gifts of food and lighting fires by graves to warm the bones of the dead who were thought to rise on night prior to the feast of All Souls. Perhaps Luther expected an audience? Dismissed. By this time the Catholic church had clamped down on such 'superstitious' practices.
Nevertheless the souls of departed loved ones would be on peoples minds at this time. I think the significance has more to do with Luther's objection to the sale of indulgences. These were spiritual IOU's which promised an accelerated passage from purgatory to heaven which the church was selling to raise money for building projects.
It's just a theory which I can't prove. Got me thinking of my Dad. At one time he'd have been interested in the mystery. In his later years his brilliant mind was diminished by years of alcohol abuse. Beautiful manners and social graces gave way to coarseness. 'Humour' became a rant of expletives. I remember one about Protestants 'squatting' in his church...He was angry up until the day he died (I think I am a bit angry too). I had a dream last night about him organising his send off in a pub called the Ship of Air. Perhaps he's moved on and I should too. I don't want to die angry.