Idolatry is the worship of an idol or a physical object as a representation of a god. In all the Abrahamic religions, and even in the Hindu scriptures, idolatry is strongly forbidden.
In Islam in particular, idolatry is ‘shirk’ (polytheism); which means attributing a partner to the Almighty God. Shirk is considered to be an unforgiveable sin in Islam. Shirk extents to and means the deification of anyone or anything other than one God. Literally, it means ascribing or the establishment of ‘partners’ placed beside God.
The Quran states: “Recall that Luqman said to his son, as he enlightened him, “O my son, do not set up any idols beside God; idolatry is a gross injustice.” [Quran 31:13]. Now, let us ask ourselves: how will we feel if we take care of a child, give him the best education, and prepare him for life, but he thanks someone else for all of these? Thus is shirk and idolatry; we are doing injustice to our Creator by associating something else to Him.
The natural instinct of monotheism that God has placed in us commands us to dedicate our worship to God Alone, and not associate anything with Him. All places of worship should be dedicated to God Alone. Belief in God includes the understanding that He alone is the worthy of worship. The Quran states “The places of worship belong to God; do not call on anyone else besides God.” [Quran 72:18]
Polytheism and idol worship were the most prominent features of the pre-Islamic Arabia, although all Arabs were the decedents of Prophet Ismael from Prophet Abraham and practiced monotheism. Each tribes had their own deities and idols.
The idol worship in Islam is considered as the most ignorant thing you can do. The conception of the entity of the Creator cannot be described by the created – this is the God that Islam seeks its adherents to believe in. The Only Being worthy of worship in Islam is the One Who created everything from nothing. When it is reduced to a form, whether an idol manifested or a thought in the restricted boundaries of the mind, it is the creation of a created being, and hence limited. But the limitations cannot be applied to the true God.
Footnote
If the argument is that the idols are for the concentration, then when a person who is about to fell into a big pit prays to God calling ‘O God’, there is no need of a picture or an idol of God because it is a call from the soul. It means that no form is needed to truly pray to the real God. Moreover, even the people who are physically blind also worship the true God without seeing any picture or idol of the God.