Reason Leads to Allah (Subhanahu Wa Ta'ala); Why Some Reject

It may be asked here: if that is the case why should people reject Allah (Subhanahu Wa Ta'ala)? First of all because many of them disbelieve in the hereafter:

Your god is one god. But those who disbelieve in the hereafter, their hearts reject (him) and they are arrogant.(16:22)

Hence even pharaoh knew for sure that Allah (Subhanahu Wa Ta'ala) is one and that he sent divine revelation. Thus Moses said to him in the course of his argument with pharaoh:

He said: in truth you know that none sent down these (portents) except the lord of heavens and earth as proofs.( 18:102 )

Another reason why some people deny Allah (Subhanahu Wa Ta'ala) is that they follow their own whims and desires:

Have you seen him who chooses for his god his own lust? Would you then be a guardian over him.( 25:43 )

And if they answer you not, then know that what they follow is their lusts. And who goes farther astray than he who follows his lust without guidance from Allah. (28:50)

Since the Qur'an confirms beyond any doubt that Allah (Subhanahu Wa Ta'ala) is one and only, so it refutes any claims of equality with Allah (Subhanahu Wa Ta'ala) who himself warns against this:

And Allah said: choose not two gods. There is only one god. So of me only, be in awe.( 16:51 )

Thus all false partners attributed to Allah (Subhanahu Wa Ta'ala) are condemned.

They surely disbelieve who say: Allah is the messiah, son of Mary. The messiah himself said: O children of Israel, worship Allah, my lord and your lord. Whoever ascribes partners unto Allah, for him Allah has forbidden paradise. His abode is the fire. For evil doers there will be no helpers. Will they not rather turn unto Allah and seek forgiveness of him. For Allah is forgiving, merciful. The messiah, son of Mary, was no other than a messenger before whom other messengers passed away. And his mother was a saintly woman. They used to eat food.( 5:73-75 )

Source: Muslim World League - Canadian Office