Through revelation from God, Muhammad (peace be upun him) liberated the human mind from superstition, deception and submission to false objects of worship as well as those concepts contrary to reason, such as the claim that God had a human son whom He sacrificed to atone for the sins of humanity.
Before the coming of Prophet Muhammad (peace be upun him), the Arab mind was dominated by many beliefs and legends incompatible with sound reason and with intellect that cannot accept what is contrary to reason. One prominent belief of the pre-Islamic period of ignorance was that stone or wood carved by people with their own hands could benefit or harm them. So, they worshiped these along with Allah or instead of Him. They feared their vengeance and intimidated their subordinates, who in turn closed their minds, unable to distinguish error from reality in such matters.
Then Allah sent Prophet Muhammad (peace be upun him) with the religion of Islam, which honored man through his intelligence and made him worthy of responsibility for religious obligations and prohibitions, while exempting the mentally deficient and the child who has not yet matured. Islam promotes and rewards one for using his mind to discover facts about the universe in the fields of science. And it prohibits everything which affects the clarity of the mind, such as various kinds of intoxicants and drugs.
Islam began by purifying religious doctrine from superstition and deception. Its creed addresses the mind, to convince it of the truth conveyed in the Qur'an and to refute the false beliefs of ignorant people, such as belief in the plurality of divinities. One example is in Allah's statement:
“Allah has not taken any son, nor has there ever been with Him any deity. [If there had been], then each deity would have taken what it created, and some of them would have sought to overcome others. Exalted is Allah above what they describe.” (23:91)
This clear argument in such concise words shows that the true God is a dynamic Creator who can benefit His servant and keep him from harm. So, if there had been more than one god, the other one would also have created and acted, so there would have been rivalry between them. One of them would then have overcome and seized the creation of the other, as do the kings of this world in their kingdoms. And when one is unable to subdue the others there can be one of three results:
Each one would hold on to his own creations and sovereignty
Some of them would eventually overcome others
All of them would be subservient to one sovereign or one God, who would have complete control over them.
The arrangement of the heavenly and earthly worlds, their interrelation and their operation according to a precise system that neither changes nor becomes corrupted is the strongest evidence that there is a single manager, besides whom there is no other deity. As it is impossible to have two equal creators for the world, it is impossible to have two objects of worship. This is but a portion of the evidence attesting to the soundness of what the Prophet of God, Muhammad (peace be upun him), conveyed regarding the oneness of divinity.
One Lord, who alone is worthy of worship, is what is most acceptable to intelligent minds. This stands out against claims that God is part of a trinity or that idols can share His divinity and His right to be worshipped alone. So, what can be greater than this crystal clear concept of monotheism, which was unknown at the time the Prophet of Mercy (peace be upun him) was sent to humanity? And what belief about God is more compatible with the sound intellect than this one?