Question 392: Why does Allaah dispraise polytheism and threaten polytheists with everlasting punishment in Hell-fire?
Answer: Allaah abhors polytheism and threatens polytheists that He will not forgive them and will cause them to undergo the perpetual residence in Hell if they die without repenting and quitting polytheism. Indeed, it is the most grievous sin and the greatest thing which Allaah prohibited. Therefore, Allaah (Glorified be He) informed us that He does not forgive its doer if he dies as a disbeliever and does not repent of his polytheistic actions. Moreover, his good deeds will be void, as none is more deviated than him... read more here.