The question of why Allah should be worshipped as one God stems from the misconceptions created around the image of God due to lack of knowledge of the concept of God and His attributes. Some religions venerate multiple gods claiming that God has different avatars or forms like humans or stones or animals, among others, while others make intermediaries or partners to God for their prayers to get answered. They elevate the creation that has no power over the universe to the level of God. 

According to Islam, Allah Almighty is the one true God who created the entire universe and what lies within it. He is unique in His attributes, His dominance prevails over all of His creation and He is the only one who sustains His creation. He sent messengers with one message: to worship Him alone without associating partners to Him. Among the reasons we worship Allah alone are as follows:

• Allah is our creator:

Allah is the sole creator of the universe and no one else makes even the smallest contribution in the process of creation. Allah states in the Qur’an: 

• “That is Allah, your Lord; there is no deity except Him, the Creator of all things, so worship Him. And He is Guardian of all things”. Surah An’am chapter 6, verse, 102.
• Do they associate with Him those who create nothing and they are [themselves] created? Surah A’raaf, chapter 7, verse, 191. 

Allah Almighty constantly reminds in the Qur’an that to Him belongs the dominion of the universe.

“Do you not know that to Allah belongs the dominion of the heavens and the earth and [that] you have not besides Allah any protector or any helper?” Surah Baqarah, chapter2, verse 107.

He alone provides us with countless blessings and sustenance on earth. 

• “[He is] Creator of the heavens and the earth. He has made for you from yourselves, mates, and among the cattle, mates; He multiplies you thereby. There is nothing like unto Him, and He is the Hearing, the Seeing.”  Surah Shura 42, verse, 11. 
• Allah - there is no deity except Him, the Ever-Living, the Sustainer of existence. Surah Al-e-Imraan, chapter 3, verse, 2. 

Allah Almighty is the sole creator and sustainer of the entire universe without any support from His creation, so He is the only one deserving of worship. Allah Almighty has challenged those who associate partners with Him in the verse:

“O people, an example is presented, so listen to it. Indeed, those you invoke besides Allah will never create [as much as] a fly, even if they gathered together for that purpose. And if the fly should steal away from them a [tiny] thing, they could not recover it from him. Weak are the pursuer and pursued”. Surah Haj, chapter 22, verse,73. 

If one contemplates they would understand that considering the universe and all that is within is dependent upon Allah Almighty who created it all and was not helped at all in doing so, against Whose ability to create there is no comparison – to the point where even we humans, no doubt the most intelligent of creatures on this Earth, cannot create even a fly, a creature so tiny and seemingly so insignificant – how can one rely upon, invoke and worship that which was created, that which is itself reliant on The Creator Who sustains all of His creation?

• There can only be one God:

If one believes that there exists more than one God governing this world, they should wonder how all of them would govern the world at the same time? One may say it should rain today while the other would say it should be a sunny day, one would decide a person should die today and the other would decree a longer life for that same person, etc. There would surely be arguments rather than coordination between the gods over the decisions regarding who would govern the universe and how as every god would want their share of dominance. There would be chaos and confusion in the universe and the world could not exist in the perfect harmony that it does. Allah states in the Qur’an: 

Had there been within the heavens and earth gods besides Allah, they both would have been ruined. So exalted is Allah, Lord of the Throne, above what they describe. Surah Anbiyaa, chapter, 21, verse, 22.

Furthermore, if there were multiple gods it would cause one to question the capabilities of God. God is perfect – free from need or assistance from anyone, unlike humans. The notion of multiple gods also arises due to the fact that humans liken God to the rulers of this world who have ministers and advisers to help them maintain their affairs. People need assistance from others to get their work done, unlike God who, according to Islam, is the all-powerful, the owner of the heavens and the earth and whatever is between them. He alone is enough to take care of all the affairs as He is self-sufficient and omnipotent, so directing our worship to other than Him yields no benefit. This is why we believe that our worship should be directed to the one true God Allah to Whom belongs the ownership of the universe as mentioned in the Qur’an.

Say, "Is it other than Allah I should take as a protector, Creator of the heavens and the earth, while it is He who feeds and is not fed?" Say, [O Muhammad], "Indeed, I have been commanded to be the first [among you] who submit [to Allah] and [was commanded], 'Do not ever be of the polytheists.' Surah An’am chapter 6, verse 14.
 

• Allah alone can grant benefit to man for his worship:

Allah states in the Qur’an: 

And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided. Surah Baqarah, chapter 2, verse 186.

Allah is the only one Who has complete control over the affairs of His creation and only He can answer our prayers, fulfill our needs and eradicate our problems. That which they have taken from God’s creation as gods besides Him are unable to support themselves, so how would they benefit mankind? The Qur’an says:

 “And those you call upon besides Him are unable to help you, nor can they help themselves." Surah A’raaf, chapter 7, verse, 197.
 
There are many verses in the Qur’an that encourage one to ponder over the reality of the nature of God, and question whether there is any benefit in exerting oneself in worship of objects or men who themselves are dependent on their creator for their needs.

Say, [O Muhammad], "Invoke those you claim [as deities] besides Allah." They do not possess an atom's weight [of ability] in the heavens or on the earth, and they do not have therein any partnership [with Him], nor is there for Him from among them any assistant. Surah Saba, chapter 34, verse, 22.

“Indeed, those you [polytheists] call upon besides Allah are servants like you. So, call upon them and let them respond to you, if you should be truthful”. Surah A’raaf chapter 7, verse 194.
 

• Allah responds to our worship directly:

Many people claim that they believe in one eternal God yet they make intermediaries of different sorts through whom they try to reach God for various reasons such as following their ancestors in making intermediaries or being afraid to ask God directly or simply because they think they can’t ask God directly. Allah says to ask him directly and He will answer one’s call in the verse:

• And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided. Surah Baqarah, chapter,2, verse, 186.
• And who is more astray than he who invokes besides Allah those who will not respond to him until the Day of Resurrection, and they, of their invocation, are unaware. Surah Ahqaaf 46, 5
• Say, "It is Allah who saves you from it and from every distress; then you [still] associate others with Him."6, 64.

Allah encourages mankind to worship Him and ask Him directly because He loves them and is the closest to them. He responds to their supplications and rids them of their problems as the only one who sees, hears and knows everything – even that which is concealed within one’s heart.

And We have already created man and know what his soul whispers to him, and We are closer to him than [his] jugular vein, Surah Qaaf, chapter 50, verse 16.

Worshipping Allah alone as one true God simplifies the life of a worshipper who can ask God directly without the confusions and complications of going through any intermediaries. In conclusion, the worship of Allah alone is the only path to success in this life and the hereafter as He is the only one worthy of worship and the only one who grants us benefit for worshipping Him. Allah knows best. May Allah guide us.