The number seven is loaded with Biblical significance. To note that God creates the world in seven days, that there are seven deadly sins, that Cain’s killer will suffer vengeance seven times over and that the Pharaoh of Egypt dreams that his land will be blighted by seven years of famine following on from seven years of plenty only begins to scrape the surface. It is also highly prominent in superstition: a person who accidentally smashes a mirror is met with seven years’ bad luck, and a witch’s cat will turn into a witch itself after seven years of service. There is also a strange ancient belief that each person undergoes a complete transformation in appearance and mind once every seven years.
Perhaps we also think once more of John Bunyan's Pilgrim's Progress. When his hero Christian sets out from the City of Destruction, he must bear on his back the heavy burden of his sinfulness. The weight of this baggage is so great that it threatens to force him down into hell.