Monotheism the inherent Creed of Mankind

Human beings by nature not only recognize the existence of a creator but instinctively reach out to Him. This is something attested to historically as well as biologically. Even those who claim atheism often recognize a belief in a higher power or a force behind nature and when faced with disaster and calamity instinctively cry out to the creator that they deny otherwise.
Islam's core belief is that not only should we recognize the existence of our Lord and creator but we should worship him alone directly without partner or intermediary as we find in the following verse of the first chapter of the Qur'an

"You alone do we worship and You alone do we seek help from" (Qur'an, 1:4)

In addition to this we must recognize God's uniqueness and not deify anything of the creation by claiming for the creation any of those characteristics which belong to the creator alone.

This core belief in God's oneness is actualized by following those messengers who he has sent throughout history from Noah to Moses and Jesus until the last of them the prophet Muhammad.

the prophet Muhammad himself stated:

‘Every new-born child is born with a pure nature. Then his parents make him a Jew, a Christian or a Magian, just as an animal is born intact. Do you observe any among them that are maimed (at birth)?

This clarifies to us that human beings are not born holding beliefs that run contrary to logic and human nature and that in fact polytheism in all its forms is unnatural. Human beings are also not born with all the answers and information need about the specifics of that they must believe and practice. For this reason God has put a natural urge in man to seek the truth and has also sent messengers to mankind human beings who convey divine revelation to mankind and teach them what to believe and how to worship their creator in preparation for the afterlife.

These two base concepts; the recognition of God as having the sole right of being worshipped and that one must worship him according to the revelation that he sent are in fact the very two things that one must testify to if they wish to become muslim.

I bear witness that none has the right to be worshiped except God (the unique creator of the heavens and the earth who does not resemble his creation) and that Muhammad is the messenger of God.