"Say: He is Allah, the One; Allah, the Eternal, Absolute; He begetteth not, nor is He begotten, and there is none like unto Him." [Quran 112:1-4]

"Every language has one or more terms that are used in reference to God and sometimes to lesser deities. This is not the case with the word ‘Allah'. Allah is the personal name of the One True God. Nothing else can be called Allah. The term has no plural or gender. This shows its exclusivity when compared to the word ‘god' which can be made plural, i.e.‘gods' or feminine, i.e. ‘goddess'. It is interesting to note that Allah is the personal name of God in Aramaic, the language of Jesus. The word Allah is a reflection of the unique concept that Islam associates with God.

To a Muslim, Allah is the Almighty, Creator and Sustainer of the universe, who is similar to none and nothing is comparable to Him. The Prophet Muhammad was asked by his contemporaries about Allah. The answer came directly from God Himself in the form of a short chapter of the Quran that is considered the essence of the Unity of God or the motto of monotheism.

"Say: He is Allah, the One; Allah, the Eternal, Absolute; He begetteth not, nor is He begotten, and there is none like unto Him." [Quran 112:1-4]

In one of the sayings of Prophet Muhammad we are told: "God is more loving and kinder than a mother to her dear child." Besides being Merciful, God is Just too. Hence evildoers and sinners must have their share of punishment and the virtuous their rightful reward. Actually, God's attribute of Mercy has full manifestation in His attribute of Justice. People suffering throughout their lives for His sake and people oppressing and exploiting other people all their lives should not receive similar treatment from their Lord. Expecting similar treatment for them will amount to negating the very belief in the accountability in the Hereafter and thereby negating all the incentives for a moral and virtuous life in this world.

Islam rejects characterizing God in any human form or depicting him as favoring certain individuals or nations on the basis of wealth, power or race. He created the human beings as equals. They may distinguish themselves and earn His favor through virtue and piety alone.

The Creator must be of a different nature from the things created because if He is of the same nature as they are, He will be temporal and will therefore need a maker. It follows that nothing is like Him. If the maker is not temporal, then He must be eternal.

But if he is eternal, He cannot be caused, and if nothing caused Him to come into existence, nothing outside Him causes Him to continue to exist, which means that He must be self-sufficient. And if He does not depend on anything for the continuance of His own existence, then this existence can have no end. The Creator is therefore eternal:

"He is the First and the Last, the Evident and the Immanent: and He has full knowledge of all things." [Quran 57:3]

He is self-sufficient or self-subsistent or, to use a Quranic term, He is Al-Qayyum. The Creator does not create only in the sense of bringing things into existence. He also preserves them and takes them out of existence and is the ultimate cause of whatever happens to them.

"Allah is the Creator of all things, and He is the Guardian and Disposer of all affairs.To Him belong the keys of the heavens and the earth: and those who reject the Signs of Allah,- it is they who will be in loss." [Quran 39:62-63]

"There is no moving creature on earth but its sustenance dependeth on Allah: He knoweth the time and place of its definite abode and its temporary deposit: All is in a clear Record." [Quran 57:3]

GOD'S ATTRIBUTES

If the Creator is Eternal and Everlasting, then His attributes must also be Eternal and Everlasting. He should not lose any of His attributes nor acquire new ones. If this is so, then His attributes are absolute. Can there be more than one Creator with such absolute attributes? Can there be for example, two absolutely powerful Creators? A moment's thought shows that this is not feasible. The Quran summarizes this argument in the following verses:

"No son did Allah beget, nor is there any god along with Him: (if there were many gods), behold, each god would have taken away what he had created, and some would have lorded it over others! Glory to Allah! (He is free) from the (sort of) things they attribute to Him!" [Quran 23:91]

In order to be a Muslim (i.e., to submit oneself to God), it is necessary to believe in the Oneness of God, in the sense of His being the only Creator, Preserver, Nourisher, etc. Having achieved this knowledge of the One True God, man should constantly have faith in Him, and should allow nothing to induce him to deny the truth. When true faith enters a person's heart, it impacts the person's outlook and behavior. The Prophet said, "Faith is that which resides firmly in the heart and which is proved by deeds". One of the striking results of faith is the feeling of gratitude towards God, which could be said to be the essence of worship." [1] 

Source:

[1] http://www.whyislam.org/877/Services/Literature/16.pdf