The killing of the innocent and auspicious bird was definitely a moral sin. There was no reason whatsoever for killing such a friendly and playful bird. He had brought a favourable south wind for the sailors. The burden of sin and guilt is too heavy to bear for the old Mariner. He wants to lighten up his burden. He is desperately in need of a person who could listen to his story. So he catches hold of one of the three wedding-guests.