Unity of God
The fundamental principle of belief in Islam is that God is One. There is No one else whatsoever in any form to be worshipped other than One God who has created this universe. There is no associate creator, no associate destroyer, neither a deputy designer nor a joint sustainer of the universe. Allah is the One and Only Creator, Destroyer, Designer and Sustainer of the universe. This is the purest form of monotheism we can ever achieve.
There are three aspects to unity of God. Foremost, that there is one Supreme being. Secondly, unity of attributes, which means that there is none having the qualities and attributes of God himself. Lastly, None is to be associated with Him in any form in prayers and worship, which means that there has to be single-minded devotion, sincerity and love for the One God and all help is to be sought form Him alone. No other being, whether living or dead, is capable of giving and snatching away anything from us. This concept frees the human mind to see the universe as it is, without fear of the sun or fire or wind and other natural forces which humans have feared all along and so resort to praying them in order to please them. With firm belief in god, man becomes aware that the natural forces are in the hand of the God and are just our contemporaries in front of God. One need not please them; instead one should please the Lord Almighty who controls them.
And know, your God is One God, there is no other, cannot be and will never be one worthy of worship but He, the Most Gracious (- Rahmân), the Ever Merciful (-Rahîm). (2:163)
Allah is One in his being, He is neither one among two nor one among three. He does not share ownership of this universe with anybody else; neither does He accept being jointly prayed to. He does not need a son or a daughter. A son ought to resemble his father in some form and has some attributes of his father. Will God handover his empire some day to the son and retire? And similarly will the son do for the grandson? And Why not a daughter? These and many such questions get resolved with the concept of unity of God. Therefore, the concept of one God is fundamental to understanding who God is.
Unity of God simply means that He is One and Alone in every sense of the word. He in unique, neither the starting link of any chain not its last link. He is above conception and conjecture, he does not have a family. Nothing is like Him, nothing resembles Him in any remotest manner, nor is He like anything else. To Him alone obedience is rendered, without Whom no affair is accomplished. He will continue to exist forever, after all creation has ceased to exist. Allah is above time, for time is also His creation. His attributes know no boundaries. Say, “(The fact is) He is Allâh, the One and Alone in His Being. Allâh is that Supreme Being Who is Independent and Besought of all and Unique in all His attributes. He begets none and is begotten by no one, and there is none His equal.” (112:1-4).