Purification of the Heart: Its Diseases and Their Cures by Imam Ibn Al-Qayyim
The heart is the ruler and the limbs execute its commands – the limbs are the implementers of its commands and are responsive to its guidance. The actions of the limbs do not materialize unless there is an objective and intention from the heart, since the heart is responsible for all of them just as every shepherd is responsible for his flock. Due to this, the concern to rectify and correct the heart should be the utmost priority for anyone seeking the right path, and analysing and remedying its illnesses should be the most important ritual that the worshippers undertake.
When the enemy of Allāh, Iblīs, learned that the heart is the focal point and is relied upon, he attacked it with whispers, presented it with various forms of temptation, and adorned for it situations and actions that would block it from the right path; providing it with a means of deviation that cut it off from the means of success. He sets traps [and lures] the heart, so that whoever escapes falling into them would not be safe from being hindered by them. So there is no escape from his traps and schemes except through constantly seeking the help of Allāh, turning to the actions that gain His pleasure, and directing the heart towards Him in its actions, inactions and sincere servitude.