Concerning his words, “to set up for Allah a rival—that is, a partner—while He created you,” he declared it the gravest of sins; for when he was asked, “Which sin is the greatest?” he began with shirk.

The Prophet (peace and blessings be upon him) also said, “Avoid the seven deadly sins.” They asked, “What are they, O Messenger of Allah?” He replied, “Associating partners with Allah, sorcery, and killing a soul that Allah has made sacred except with due right …” and he completed the list.

He opened the enumeration with shirk, which proves that shirk is the most serious of all sins. For that reason a polytheist will never enter Paradise. Allah the Exalted says: “Whoever associates anything with Allah, Allah has forbidden Paradise to him, and his refuge will be the Fire. The wrongdoers shall have no helpers” (al-Māʾidah 5:72).

Likewise, Allah does not forgive the one who commits shirk: “Indeed, Allah does not forgive that partners be ascribed to Him, but He forgives whatever is less than that for whom He wills” (al-Nisāʾ 4:48). This proves both that Paradise is forbidden to the polytheist and that Allah will not pardon him. It further shows that shirk is the gravest of sins, for every sin other than shirk is eligible for pardon: “Indeed, Allah does not forgive that partners be ascribed to Him, but He forgives whatever is less than that for whom He wills.”

Adultery, theft, drinking wine, and usury all fall under this divine will: if Allah so wills, He will forgive the offender; and if He wills, He will punish him.