What is the significance of the closed door that would protect `Umar from afflictions discussed by Prophet Muhammad (peace be upon him)?
 Narrated Abu Wail:                     Hudhaifa said, "`Umar said, 'Who amongst you remembers the statement of Allah's Apostle (p.b.u.h) about afflictions'?' I said, 'I know it as the Prophet had said it.' `Umar said, 'No doubt, you are bold. How did he say it?' I said, 'A man's afflictions (wrong deeds) concerning his wife, children and neighbors are expiated by (his) prayers, charity, and enjoining good.' (The sub-narrator Sulaiman added that he said, 'The prayer, charity, enjoining good and forbidding evil.') `Umar said, 'I did not mean that, but I ask about that affliction which will spread like the waves of the sea.' I said, 'O chief of the believers! You need not be afraid of it as there is a closed door between you and it.' He asked, 'Will the door be broken or opened?' I replied, 'No, it will be broken.' He said, 'Then, if it is broken, it will never be closed again?' I replied, 'Yes.' " Then we were afraid to ask what that door was, so we asked Masruq to inquire, and he asked Hudhaifa regarding it. Hudhaifa said, "The door was `Umar. "We further asked Hudhaifa whether `Umar knew what that door meant. Hudhaifa replied in the affirmative and added, "He knew it as one knows that there will be a night before the tomorrow morning."