Ibn al-Jawzi made an exceptionable parable about this battle between man and Shytaan. He said in Talbees Iblees,
The heart is like a fort that is surrounded by a wall and the wall has gates from which it can be torn down. In it lies the mind. The angels frequent that fort and next to that fort are places where the desires lie. And the devils enter into this surrounding area without being prevented from doing so. And the war exists between the inhabitants of the fort and the inhabitants of the surrounding areas. The devils never stop circling the fort and looking for an opening where the guard is heedless and from where he can tear down the fort.
It is obligatory for the guards to be completely aware of all of the gates of the fort that must be guarded as well as all of its weak points from which destruction can come. The guard cannot take a break because the enemy never takes a break. A man sai al-Hasan al-Basri, “Does Iblees sleep?” He answered, “If he were to sleep we could then have a rest.”
The fort is lit by the remembrance of Allah and faith in Him. In it is a polished looking glass through which [the guardians] can then see anything that passes by. The first thing that Shytaan does is to blow smoke into the fort to make its walls black. This causes rust and damage in the fort. Sound thought repels Shytaan and remembrance of Allah cleans the looking glass. The enemy has carriages and sometimes they are able to enter the fort. The guards may come upon them and force them to leave. Perhaps they may enter due to the heedlessness or carelessness of the guards. Perhaps, due to the smoke and the rust, Shytaan enters through any way and he is not perceived. Perhaps the guard is injured by the heedlessness or is taken prisoner and led to the following of the desires. ‘
Source : The world of Jinn and Devils – by Umar S. al-Ashqar