In the tradition from Imam Reza (a.s.) where he has listed the Greater Sins, despondence is mentioned after despair (Yaas). Qunut (despondence) is described as the condition where one's heart loses hope of Allah's Mercy and that person does not even dislike the hopelessness. According to the religious scholars the difference between Yaas and Qunut is that the term 'Yaas' is used in general cases and 'Qunut' in special cases. It means that 'Yaas' describes the internal condition of one's heart. When this internal hopelessness intensifies to a degree whereby its effect becomes manifest outwardly and seem obvious to the common people, it is called 'Qunut'.
In short whoever expresses hopelessness by his speech or actions is actually a victim of 'Qunut'.
Hopelessness in Dua is Yaas
Many scholars believe that to discontinue invocation is a sign of despair. The hopeless person believes that he will not reach his destination through dua.
'Qunut' means that one accuses Allah of not being merciful and for not accepting his repentance. He thinks that whatever difficulties he suffers, are the retribution of his sins. Thus Imam Sajjad (a.s.) says in the 39th Dua of Sahifa-e-Sajjadiyah, "I neither despair of Your Mercy nor am I in despondence regarding you. But I am aggrieved because my good deeds are less in number and bad deeds numerous. Otherwise Your position is so high that not a single creature turns away dejected from you."
There is no doubt that despondence with regard to Allah is a Greater Sin. It is one of the characteristics of the polytheists and hypocrites as mentioned by Allah in Surah Fath.
"And (that) He may punish the hypocritical men and the hypocritical women, and the polytheistic men and the
polytheistic women, the entertainers of evil thoughts about Allah..."
(Surah Fath 48:6)
Skepticism Invites Punishment
The Holy Prophet (s.a.w.s.) announced from the pulpit
"By Allah who has no partner, He does not deprive any of the people from the blessings of this world and the hereafter.
But he should not harbour doubts (about Him). He should have hope in Him and possess good morals. He should refrain from backbiting about the believers. I swear by Allah Who is the One and
without partners, He does not punish a believer after he had repented and asked for forgiveness. Except those who are skeptical about Allah and lack in hope, have evil behaviour and indulge in
backbiting about the believers. I swear by Allah except Whom no one is fit to be worshipped. When someone expresses reliance and trust in Allah; Allah who is extremely graceful, will not deem it
fit to order anything contrary to the faith that the believer has reposed in him. Then you must have good thoughts regarding Allah and must always depend upon Him."
Hope For Forgiveness and the Acceptance of Dua
Having good thoughts about Allah means that one should have the conviction that if he repents for a sin, Allah would forgive him. If he invocates, his prayer would be answered. If he does a good action, it is certain that Allah would accept it and reward him for the same. To hope in salvation is beneficial, and it is obligatory. However to hope for rewards without performing good actions is ignorance and conceit.
Hopelessness in the Affairs of This World and the Hereafter
Some scholars of religion explain that the distinguishing feature of 'Qunut' and 'Yaas' is that 'Qunut' denotes hopelessness with regard to the worldly blessings.
The Holy Quran says concerning this,
"And He it is who sends down rain after they have despaired, and He unfolds His Mercy; and He is the Guardian, the Praised One."
(Surah Shura 42:28)
Concerning 'Yaas' the scholars maintain that it is with regard to the affairs of the Hereafter, as mentioned in the
"...indeed they despair of the Hereafter..."
(Surah Mumtahena 60:13)
Qunut is Worse Than Yaas
To be despondent of Allah's Mercy results in the person being deprived of eternal blessings, because 'Qunut' causes the severance of the relation between the creature and Allah. The cause for this despondence is the extinguishing of the original flame of creation that had been alive in his heart. Even if a little of the light had remained, he would not have lost hope completely. It is possible that he may be involved in vain pursuits. If that is so then he has receded into the age of ignorance from the Mercy of Allah. But 'Yaas' denotes that the connection between the creature and Allah still remains even though separated by the curtain of sins. But behind the curtain the light of the original nature endures. He still believes in some connection with Allah. In such a case the dividing curtain could be removed.
'Yaas' can be forgiven but 'Qunut' does not deserve forgiveness. Thus 'Qunut' is included in the title of Shirk and becomes the greatest danger for man. (Quoted from Tafsir Ruhul Bayan)