While associating partners with God (shirk) is the greatest unforgivable sin, despairing of Allah's mercy is a very grave sin, characteristic of disbelievers, hindering repentance and access to His infinite mercy.
In the sublime teachings of the Holy Quran, no sin is considered as great and unforgivable as shirk, which is associating partners with Allah. Numerous verses explicitly state that Allah does not forgive the sin of shirk unless one repents and embraces faith before death. This underscores the paramount importance of Tawhid (Oneness of God) in Islam. However, despairing of Allah's mercy (Qunut), although not explicitly labeled as 'the greatest sin,' is considered a very grave and dangerous transgression in the Quran, characteristic of disbelievers and the misguided. This despair is a sign of weak faith and a lack of proper understanding of God's perfect attributes, especially His vast mercy and infinite forgiveness. When an individual despairs of Allah's mercy, they are essentially doubting His power and forgiveness, which can lead to severe spiritual and practical consequences. The Holy Quran unequivocally forbids believers from despair. In Surah Yusuf, verse 87, Prophet Jacob (peace be upon him) advises his sons: "O my sons, go and find out about Yusuf and his brother and do not despair of the relief of Allah. Indeed, no one despairs of the relief of Allah except the disbelieving people." This verse clearly indicates that despairing of divine mercy is a characteristic of disbelievers and unbelievers, not of the faithful. Despair, in essence, is an implicit denial of one of God's most crucial attributes, 'Ar-Rahman' (The Most Merciful) and 'Ar-Rahim' (The Especially Merciful). One who despairs of Allah's mercy seemingly believes that their sins are too great to be forgiven by God, or that Allah is unable to help them. This notion limits the divine essence of Allah, whose power and mercy are infinite. Another critically important verse in this context is Surah Az-Zumar, verse 53, known as the 'Verse of Hope' (Ayat al-Rajā'): "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" This verse unequivocally opens the doors of repentance and return for all sinners, even those who have committed many transgressions. Despair of divine mercy is essentially a barrier that a person constructs between themselves and this boundless ocean of divine grace. If an individual despairs of God's mercy, they lose the motivation to repent and reform themselves, thinking that their sins will not be forgiven. This leads to further immersion in sin and corruption, blocking the path to reform and spiritual growth. The Prophet Muhammad (peace be upon him) also emphasized the importance of hope in divine mercy and avoidance of despair in numerous hadiths. Despair is not only spiritually damaging but can also psychologically lead an individual towards depression, apathy, and even the commission of more sins. A despondent person feels worthless and might believe that efforts to improve their situation are futile. This state prevents them from moving forward on the path of righteousness and success. In summary, although shirk is named as the greatest sin in the Quran and is the only sin that is not forgiven without repentance and turning back to God, despairing of Allah's mercy is also a very grave and dangerous major sin. The reason for this is that despair stems from a lack of proper knowledge and faith in Allah and can close the doors of repentance and reform for a person. Despair deprives an individual of drawing closer to Allah and benefiting from His grace and mercy, sending a message that Allah, contrary to what He has revealed, is not Forgiving and Merciful. Therefore, while shirk effectively severs a person's relationship with God, despair weakens this relationship and prevents its restoration. A true Muslim must always maintain a balance between fear of divine punishment and hope in His mercy; for Allah is both "Severe in Penalty" (Shadid al-Iqab) and "Most Forgiving, Most Merciful" (Ghafurur Rahim). Maintaining this balance prevents falling into the abyss of despair or undue pride, paving the way for success in this world and the hereafter.
O my sons, go and find out about Yusuf and his brother and do not despair of the relief of Allah. Indeed, no one despairs of the relief of Allah except the disbelieving people.
Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'
He said, "And who despairs of the mercy of his Lord except those astray?"
They say that in ancient times, a man, after committing many sins, became so disheartened and distressed that he lost all hope of mercy. He spent his days and nights in sorrow and believed that God would never forgive him. One day, he came upon a wise man whose wisdom was renowned throughout the lands, and he recounted his state. The wise man, with a kind smile, said: "O young man, you are oblivious to the ocean of Divine Mercy, whose vastness exceeds all your sins. Have you not heard that God has said: 'Do not despair of My Mercy?'" Then the wise man told a story of a virtuous person who, in his youth, had made many mistakes but never lost hope in God and constantly repented at His threshold. The wise man continued: "With every tear of remorse he shed, a speck of the rust of his sins was removed, until his heart became as pure as a mirror, and he reached the status of true penitents. So, my friend, do not drown in this boundless sea, for the ship of salvation is hope, and its oar is repentance." Upon hearing these words, the man's heart was illuminated; he prostrated himself and repented from the depths of his being. From then on, with hope in Divine Mercy, his life transformed, and he recounted this tale to anyone who harbored despair in their heart.