What does this word mean in the Qur'anic context?
Firstly, "polytheism" or "idol worship" is a poor, narrowband translation of "shirk" which implies that multiple gods or another god replaces the one God.
The Qur'an defines shirk as association or partnership with God, meaning that God is not totally replaced, but someone or something is placed alongside God to give that someone or something the power to add to, remove, or change religious commandments and/or prohibitions.
22:26 is the general rule: Do not associate with Me anything
The Qur'an presents many examples of things people associate with God (19:81) - they include:
🔹 other names besides God’s name (19:65, 39:45, 40:12),
🔹 pagan gods and goddesses (53:20),
🔹 statues for veneration (7:138-139),
🔹 intercession on Judgment Day (30:13),
🔹 dead prophets and saints (3:79-80, 16:20-21, 35:14, 46:5-6),
🔹 the scripture itself (6:19),
🔹 ancient images, icons, and shrines (35:13-14, 7:194),
🔹 golden calf (7:148-150),
🔹 money, wealth, and children (18:42, 7:190),
🔹 own ego and selfish desire (25:43),
🔹 uncontrolled libido (24:3),
🔹 wishful thinking (45:23),
🔹 destructive urges in the human psyche (14:22),
🔹 languages (14:4),
🔹 places or buildings (22:26),
🔹 celebrities, cult figures, spiritual leaders, religious scholars, prophets (9:31)
and so on …
All these can subvert our internal guidance (Zikr) if we allow them to, and present as a case of ‘association’ or ‘shirk’ (19:65). But we humans are all inclined to or involved in shirk in one form or other, especially with the belief in God (12:106).
A simple and clear example
There is no prohibition on eating reptiles (lizards, snakes) in the Qur'an. However, based on narrations, "ulema" have declared that reptiles are prohibited as food in the religion. By following this edict, a new religious law has been added, so anyone following it has appointed the ulema issuing the fatwa as an associate of God (9:31) - and fallen into shirk.
In general, any law, commandment, or prohibition that is not already stated in the Qur'an constitutes an entry into shirk for every follower of that law, commandment, or prohibition.
Effect of shirk
Allowing others to overcome the internal guidance God has placed in all of us (30:30, 91:7-10) has grave effects on our ability to interact with the real world. We are diverted from our intellect and conscience when making decisions - and God has said that our ventures will fail 24:55 God has promised that those of you who will believe in the Divine laws and strengthen human resources, He will make them rulers on earth, as He granted rule to the previous nations. He will certainly establish for them the System of Life that He has approved for them, and will replace their fear with peace and security. All this because they obey Me alone. They ascribe no partner to Me. But all those who, after this, deny these laws will drift out (of the community of living nations).
Dr Shabbir notes in his tasreef - [28:6, 33:27. The ‘belief’ mentioned in this verse does not pertain to any dogmas and tenets, but to the realization that the entire Universe is operating under the changeless physical laws of One Supreme Authority, thus providing the basis for all science and technology]
Furthermore, it is the one sin God will not forgive
4:116 God will not forgive Shirk (choosing ‘authorities’ besides Him), though He may forgive other transgressions according to His law of forgiveness. Whoever commits Shirk, has strayed far, far away
But the Qur'an also notes that it will be difficult for people who have associated to disassociate
42:13 He has ordained for you all, the same System of Life that He enjoined upon Noah - And We have revealed to you the same message as We enjoined upon Abraham, Moses, and Jesus: "Establish the Divine System of Life and make no sects in it.” The unity you call to, it is hard upon the associators. God draws to Himself everyone who is willing, and guides to Himself everyone who turns to Him for guidance.”
Most people do not realize that they are associating
On the Day We assemble them, We will ask the associators, “Where are now those partners of God that you conceived?” They will hardly have a response, but they will swear," By God, our Lord, we were never associators.” (6:22-23)
A dire warning
12:106 The majority of people do not believe in God without remaining associators
This is because most people who believe in God are also adherents of one man-made religion or other - based on a human prophet or messenger - and deviated from the Way (Deen).