The third verse indicates why the hypocrites behave so foolishly and why they fail to see the folly of their course:

فِي قُلُوبِهِم مَّرَ‌ضٌ فَزَادَهُمُ اللَّـهُ مَرَ‌ضًا

In their hearts there is a malady, so Allah has made them grow in their malady.

Now, illness or disease, in the general medical sense, is a state in which a man has lost the balanced proportion of the elements within him necessary to keep him healthy, so that his body can no longer function properly, which may finally lead to his total destruction. In the terminology of the Holy Qur'an and the Hadith, the word 'disease' is also applied to certain mental or psychic states (we are using the two terms in the original and more comprehensive sense) which hinder man from attaining any degree of spiritual perfection, for they gradually deprive him of the ability to perform good deeds, and even of ordinary human decency, till he meets with his spiritual death. The great spiritual master, Junaid of Baghdad, has said that just as the diseases of the body arise from an imbalance among the four humours, the diseases of the heart arise from a surrender to one's physical desires. According to the present verse, the disease hidden in their hearts is unbelief and rejection of the truth, which is as much a physical sickness as a spiritual one. It is all too obvious that being ungrateful to one's creator and nourisher and going against His commandments is to be spiritually sick. Moreover, to keep this disbelief concealed for the sake of petty worldly gains and not to have the courage to speak out one's mind is no less a disease of the soul. Hypocrisy is a physical disease too in so far as the hypocrite is always shuddering4for fear of being exposed. Jealousy being a necessary ingredient of hypocrisy, he cannot bear to see the Muslims growing stronger in the world, and yet the poor hypocrite cannot even have the satisfaction of unburdening his heart of the venom. No wonder that all this tension should express itself in physical ailment.

The curse of telling lies

(4) There is another subtle and very significant point here. According to these verses, the hypocrites would meet with a grievous punishment for having told lies. Now, their greatest crime was disbelief and hypocrisy in matters of faith, and they had been committing other crimes as well, like nursing envy and malice against Muslims in their hearts and actually conspiring against them. And yet here the grievous punishment has been connected with their habit of telling lies. This is an indication that basically this nefarious habit was their real crime, which gradually led them to hypocrisy and disbelief. In other words, although hypocrisy and disbelief are much greater crimes, yet they arise from the habit of telling lies. That is why the Holy Qur'an combines the sin of lying with the sin of idol worship in the same phrase:

فَاجْتَنِبُوا الرِّ‌جْسَ مِنَ الْأَوْثَانِ وَاجْتَنِبُوا قَوْلَ الزُّورِ‌

"Guard yourselves against the filth of idols and against telling lies" (22:30)