The religion of Islam is based on a core belief that there is no god worth worshiping except Allah. If someone accepts Islam, or if a Muslim wants to renew or confirm his or her faith, they confess their belief that there is no god worth worshiping except Allah and that Muhammad is His last Messenger. Ashadu an la ill laha il Allah wa Ashadu anna Muhammadan Rasulullah. Saying these words, the Creed, is the first of the five pillars or foundations of the religion of Islam. Belief in God is the first of the six pillars of belief. 
Muslims believe that there is only one God. He alone is the sustainer and the creator of the universe. He has no companions, children or partners. He is the Most Merciful, the Most Wise and the Most Just. He is the all-hearing, all-seeing and omniscient. He is the first, he is the last.
„Say:“ He is God, only one, God, the Absolute (eternally independent, on whom everything depends). He does not produce and has not been created and none is equal to Him. “ (Quran 112)
“Creator of heaven and earth! How should He have a son where He has no companion and where He created everything and knows all things? He is Allah your Lord. La ilaha illa Huwa; it is not a god but Him (alone), the creator of all things; so worship Him. And He is the keeper of all things. Looks cannot reach him, but he does reach the looks. And He is the All-Kind, the All-Known. ” (Quran 6: 101-103)
This belief is sometimes called monotheism, a word derived from the Greek words ‚monos‘, the only one, and ‚theos‘, which means God. It is a relatively new word in the English language and is used to refer to a higher being who is almighty, the one who is responsible for life, the one who rewards or punishes. Monotheism is the direct antithesis of multiple gods, the belief in multiple gods, and the antithesis of atheism, the unbelief in all gods.
If we consider the general meaning of the word ‚monotheism‘, this could include Judaism, Christianity, Islam and Zoroastrianism, as well as some Hindu philosophies. However, the monotheistic religions usually refer to Judaism, Christianity and Islam and group them together; although there are significant differences between Christianity and Islam.
The concept of the Trinity, which is inherent in most Christian denominations, is said to include aspects of plurality. The belief that a god somehow consists of three deities (father, son and holy spirit) contradicts the concept of monotheism, which is peculiar to Islam, where the unity of God cannot be questioned. Some Christian groups, including those known as Unitarians, believe that God is one and cannot be God and man at the same time. They take the words of Jesus literally in John 17: 3. However, the vast majority of Christians do not share this belief.
In the religion of Islam, belief in One God, without companions or partners, is essential. It forms the center of religion and is the core message of the Quran. The Quran calls on humanity to serve only God alone and to give up worshiping false gods or companions. The Quran asks us to look at the wonders of creation and understand the greatness and power of God, and it speaks directly of His names, qualities, and deeds. The Quran commands us to reject anything that is worshiped instead of or next to God.
„And I (God) created the Ginn and the people only so that they (should) serve Me.“ (Quran 51:56)
Islam is often referred to as pure monotheism. It wasn’t spoiled with strange concepts or exaggerations. Belief in the One God brings certainty. Muslims worship God alone, He has no companions, side gods or helpers. Worship is directed to God because He is the one worthy of worship. There is nothing bigger than God Alone.
„Say:“ All praise is due to God, and peace be upon those of His servants whom He chose (deliver His message). Is God better or what they worship (instead of His)? “ (Of course God is better!)
Who created heaven and earth, and who sends down water from heaven for you, through which we let beautiful gardens sprout in beauty? You cannot let their trees sprout. Does God exist alongside God? No, they are a people who place gods next to God.
Who made the earth a resting place and led rivers through its middle and founded solid mountains on it and set a barrier between the two seas (salty and sweet)? Does God exist alongside God? No, most of them don’t know.
Who answers the afflicted when he calls him, and takes away the evil and makes you followers on earth? Does a god exist alongside god? What you consider is minor.
Who guides you in the darkness over land and sea, and who sends the winds as messengers of joy before His mercy? Does a god exist alongside god? God is exalted above what they associate with him.
Who then creates and repeats creation at the beginning, and who cares for you from heaven and earth? Does God exist alongside God? Say: „Bring your proof if you are truthful.“ (Quran 27: 59-64)
 The six pillars of faith are belief in God, His angels, His prophets and messengers, all of His revealed books, the day of judgment and divine predestination.