It is stated in very clear terms in the Quraan:
بَدِيعُ السَّمَاوَاتِ وَالْأَرْضِ أَنَّى يَكُونُ لَهُ وَلَدٌ وَلَمْ تَكُنْ لَهُ صَاحِبَةٌ وَخَلَقَ كُلَّ شَيْءٍ وَهُوَ بِكُلِّ شَيْءٍ عَلِيمٌ • ذَلِكُمُ اللَّهُ رَبُّكُمْ لَا إِلَهَ إِلَّا هُوَ خَالِقُ كُلِّ شَيْءٍ فَاعْبُدُوهُ وَهُوَ عَلَى كُلِّ شَيْءٍ وَكِيلٌ [الأنعام: 101-102]
“(He is) the Originator of the heavens and the earth. How can He have a son when He never had a wife? He created everything, and He knows everything. This is Allah: your Lord, there is no God but He, the Creator of everything; so, worship Him. He is Guardian over everything.” (Al-An’aam:101,102)
Another Aayah (Verse) — the very first Aayah of the Quraan — revealed to the Holy Prophet Hadhrat Muhammad (SallAllaho ‘Alaihe WaSallam) states:
اقْرَأْ بِاسْمِ رَبِّكَ الَّذِي خَلَقَ [العلق: 1]
“Read with the name of your Lord who created (everything).” (Al-Alaq:1)
Islam is a religion of knowledge. Knowledge in Islam is only dictated through the One who perfected the brain and blessed us with the ability to comprehend. All human beings regardless of religion, color, sex, social status, political affiliation, wealth, etc., with the ability to comprehend have been encouraged by the Creator to contemplate their surroundings and themselves to see the beauty and perfection of the Originator.
After understanding that it is the Creator alone who creates everything, the human being is instantly reminded by the Lord that he/she has always been and is being sustained and provided for by the Supreme, and none other. When we fail to acknowledge the clear signs of the Lord’s existence, we disregard ourselves.
For instance, if we could care less about the most amazing phenomena of day and night that we witness every morning and evening, it clearly shows our failure in being so busy with worldly affairs that we have not even had a moment to look at the huge sky above our heads. If we have looked at it, have we not been alarmed by the fact that it holds firmly, layer after layer, without millions of pillars or support. (Ever seen a roof without any support?) This is only one of His signs of existence and this leads us to the ultimate reality as pointed out in the above quoted Aayaat of the Quraan. It is through divine knowledge that Islam enlightens us to the reality that the Creator does not in any way resemble His creation! Is it not necessary to know the owner before we worship Him?
Or, how about considering the sun, the moon and the stars? There is no need to get the telescope out. The signs of the One who created us and all other things around us are clearly displayed for all to see. If these heavenly bodies amaze us then have we considered the One who perfected them? His Majesty is irresistible, so how can we accept others as gods and associate to Him when He has not asked us to? How can we look at those things and refer to them as gods when we can’t even bear to look at just one of His signs; the sun?
Just having spoken about these signs, the intelligent hastens to repent before the most-forgiving and cries out at all times to the all-hearing and the all-seeing:
إِيَّاكَ نَعْبُدُ وَإِيَّاكَ نَسْتَعِينُ [الفاتحة: 5]
“You alone do we worship, and from You alone do we seek help.” (Al-Faatihah:5)
And this is whom Islam commands all human beings to worship and hence Islam is termed a universal religion. And yes, the last and final Prophet – the Prophet of Islam — Hadhrat Muhammad (SallAllaho ‘Alaihe WaSallam), was sent by Allah (Subhaanahu Wa Ta’aalaa) like the other Prophets before him, as a bearer of the good news and as a warner to all mankind. Islam recognizes that all human beings are the children of Prophet Hadhrat Adam and Hadhrat Hawwaa (Eve) and this frees Islam from accusations and allegations directed towards it. It also places a hefty responsibility on the Muslims to practice and present Islam as He has revealed and much of the blame today lies with the Muslims and in their failure to live Islam as shown by their beloved Prophet Hadhrat Muhammad (SallAllaho ‘Alaihe WaSallam).
Having understood, the human being who is filled with awe and zeal to learn more about his Lord, is ordered by Him to worship Him alone, without any associates whosoever. Oh, but I could care less you say! Well then consider this, it is to the Originator that all things return, and this is not rocket science either. The good news and the warning is that one day we will not be able to escape from death and its time has been appointed by the all-knowing just like the time of our birth was fixed, not a second later and not a second earlier. Then what?