Let me ask you a question, When you buy a new device,why does the manufacturer put a user manual with it ?
Let me answer this for you :
to point out how to make that device work properly, smoothly and not to be damaged easily.
If this is the case with any device, how about humans?
Are not they manufactured (created) by God?
As The Creator knows best what benefits or harms his creations, he sent books ( as user manuals) to be a guide and a reference for them on how to live properly.
Now, how can any reasonable person claim that the books (user manuals) are not important, and that we can just live our life in our own terms?
I think a reasonable person will follow the book to lead a healthy happy life and he will thank his Creator for guiding him and not leaving him without reference for proper life.
The Creator is Allah
The device is man
User manual is Qur'an (as the last and only preserved, unchanged book ).
The delivery men are messengers of God.
So, if you like to live happily and properly, you can't say I will leave the Books of my Creator, and I will worship him in my own way.
Not only because your life will not work properly but also because God will not accept that.God accepts from us only when we follow his rules that are mentioned in his book. Nothing more and nothing less.
So if we accept to worship God, let's worship him as he accepts ; in his own rules.
Allah (Almighty God) The Creator said clearly and definitely that he only accepts Islam.
As Allaah said:
Whoever seeks a way other than Islam, it will never be accepted from them, and in the Hereafter they will be among the losers.
I think no one would like to be among the losers.
God made it clear, for anyone who likes to live properly as God commanded in his book,
God accepts Islam only.
And Islam means total submission and obedience to God.
This was the message for all humans in all the divine books. All prophets were Muslims.
So, to be successful, just follow the steps in the book
Indeed, the religion in the sight of Allah is Islam. And those who were given the Scripture did not differ except after knowledge had come to them - out of jealous animosity between themselves. And whoever disbelieves in the verses of Allah, then indeed, Allah is swift in [taking] account