explain coleridge's use of a frame story to present the tale of the mariners adventure

The frame Story Coleridge uses is the whole wedding party guest scene. The Mariner stops a guest and tells him the supernatural story. I suppose the guest isn't too creeped out by this old guy going into detail about the Mariner's adventure. The guest makes comments throughout the story expressing fear and astonishment so the story had an effect on him. The wedding guest eventually misses the wedding but goes away wiser. I'm not sure if the guest loved sea snakes but I think he got the point. This story frame gives the Mariner's tale a mysterious feel as the guest isn't repelled by this old guy but rather transfixed by his tale.