In Islam, shirk is a sin in the form of the practice of idolatry or polytheism, that is, deification or worship of someone or anything other than the only God, that is, Allah. In the literal sense, this means the establishment of “intermediaries” between man and God. This is a vice that contradicts the virtues of Tawheed (monotheism). Those who practice shirk are called mushriks. Simply put, mushrik is a pagan. In Islamic law, shirk as a crime can only be attributed to Muslims, since only a Muslim is legally responsible for such apostasy.
Etymology
The word širk comes from the Arabic root Š-RK (ش ر ك) with the common meaning of "share." In this context, Mushrik is one who “shares” the power and greatness of Allah with other entities or people who act as intermediaries.
Islamic commentators of the Qur'an emphasized that pre-Islamic Arab idolatry worshiped several goddesses (the most memorable of them - al-Manat, al-Lat and al-Uzza) as equal companions of Allah. Therefore, Mushrik is primarily a polytheist, an idolater.
Other sins
Other forms of idolatrous sin in Islam include worship of wealth and other material objects. This is stated in the Qur'an in one of the stories about the children of Israel, who created the Golden Calf as an idol, for which Moses ordered them to repent.
Another form of idolatry mentioned in the Qur'an is the deification of spiritual leaders, gurus, and prophets (except for Muhammad). People following the false prophets are mushriks. They are actually equated with pagans and apostates.
Medieval Muslim (as well as Jewish) philosophers identified faith in the Trinity with the Shirk heresy. For according to Muslim beliefs, Allah is one and does not need intermediaries.
Allah's partners
In a theological context, a person sins by connecting some lesser being with Allah. This sin is committed if you imagine that God has a partner who can be worshiped. What is said in the Qur'an? The fact that Allah does not forgive when he is assigned some spiritual partners or “companions”, but at the same time he forgives everything, anything, anyone. However, the assignment of partners to him, as the mushriks do in Islam, is one of the most serious misconduct. The boundaries of the concept of idolatry are quite flexible, and theologians often describe the excessive veneration of an artifact here on Earth as an example of idol worship. Some orthodox Islamists, for example, claim that the faithful who worship the Kaaba in Mecca are mushriks.
Atheism
Atheism is also perceived by Muslims as a deviation from the true faith, because it denies the position of Allah as the unique creator and bearer of the Universe (Tawhid ar-rububiyya, Unity of Dominance), and people who claim to be atheists are punished in Muslim countries. In the same way, the act of evasion extends to such things as the idea that God has human anthropomorphic qualities, as well as acts of worship or piety, the internal purpose of which is pride, whim, or desire for public admiration, although public prayer is the main Islamic aspect faith supported and praised in the Qur'an.
Other Abrahamic religions
The status of the “people of the Book” (ahl al-kitab), especially Jews and Christians, regarding Islamic beliefs about unbelief is not clear. Charles Adams writes that the Qur'an blames the “people of the Book” for rejecting the message of Muhammad, although they should have been the first to accept it as the holders of earlier revelations. Muslims especially distinguish Christians for neglecting the concept of the unity of God. Verse 5:73 of the Qur'an (“Of course, they do not believe [Kafar] who says: God is the third of three”), among other verses, is traditionally perceived in Islam as a rejection of the doctrine of the Christian trinity, although modern science offers alternative interpretations of this passage.
Other verses of the Qur'an categorically deny the divinity of Jesus Christ, the son of Mary, and reproach people who regard Jesus as God, promising all Christians eternal punishment in hell. The Qur'an also does not recognize the status of Jesus as the Son of God or God himself. At the same time, Muslims respect him as a prophet and messenger of the Most High, sent to the children of Israel.
Historically, the "people of the Book" (Jews and Christians), permanently residing under Islamic rule, were entitled to a special status known as dhimmi. They were allowed to practice their religion, but they were forced to pay a special tax for this.