By Imaam Ibn al-Qayyim.
Among its (the sins) effects is that the disobedient sinner is constantly in the shackles of his Shaytaan and the prison of his shahwa (desires) and the chains/ fetters of his hawaa (whims). So he is a captive, one who is imprisoned and who is tied up. There is no captive in a worse state than the one who is captivated by his worst enemy and there is no prison which is tighter than the prison of hawa (desire) and there is no bond/ fetter more strong than the bond of desire.
How, then, will a heart which is captivated, imprisoned and fettered travel unto Allaah and the Home of the Hereafter?
How will a person take a single step forward when the heart is bound and harmful things approach it from every direction?
The example of the heart is like the example of a bird. Every time is ascends it becomes distant from the harmful things and every time it descends the harmful things hurt it. In a hadeeth there occurs that Shaytaan is like a wolf to people. Just as when a sheep has no protector and is in between many wolves, they are quick in causing damage and injury; likewise the servant who does not have guardianship from Allaah, then his wolf (i.e. his desires, whims etc.) is to him a predatory animal. Thus there is no escape for the servant from having protection from Allaah. Taqwaa (fearing Allah) is a safeguarding for him and a strong shield between himself and the punishment of this world and the Hereafter.
Every time the sheep is close to its shepherd it is safer from the wolf and every time it becomes distant from its shepherd it is closer to destruction. So its sanctuary is when it is close to its shepherd because the wolf takes the lonely one from the flock and this is the one which is the furthest one of the flock from the shepherd. The basis of all of this is that every time the heart is distant from Allaah the harmful things are quick in approaching it and every time it is close to Allaah the harmful things become distant from it.