He (SWT) created this world so as to facilitate man and djinn to worship Him.
After creating us He (SWT) asked us whether He (SWT) is our sustainer or not.
We all agreed that this is the absolute truth.
The He (SWT) said that He (SWT) will send us to this world for a while and we should not forget this admission that He (SWT) is the One who sustains us.
That He (SWT) sustains us, the whole whole world, He (SWT) is One, absolutely independent of everything, neither is begotten nor begets, He (SWT) is the only one worthy of worship is called the doctrine of Unity of God. This is one of the three fundamental assertions of the religion of Islam.
Some people assert that all paths are correct, they all lead to the same goal.
Because of obvious contradictions between different religions this can not be the truth.
Clearly one has to decide which religion is the true religion.
The two other main assertions of Islam are the principle of Prophethood and the concept of Hereafter.
After coming to this world we forget the promise we made to God, Allah, Eeshwar, Bhagwaan that He (SWT) alone is the One who sustains us. We get involved in this world as if this is our final destination - which it is not. So Allah (SWT) sends us His Messengers or Prophets who tell us what is the correct religion and how to live in this world. His method is that He (SWT) chooses one of us and then communicates His message to him through His angel. The Prophet in turn tells us the message. Allah (SWT) has sent Prophets to all communities of the world. This means that He (SWT) must have sent, in all probability many, messengers to India too.
This series of Prophets was terminated with beloved Prophet Muhammed (PBUH). Now the religion, the true religion is preserved in his life history and the book that was revealed to him. The book was revealed to him, he did not write it. May Peace and Blessings of Allah (SWT) be upon him.
This is the concept of Prophethood in Islam.
Finally there is the concept of heaven and hell. This is the concept of hereafter. We also call it Aakhirah.
This is completely familiar in India. Heaven is called Swarg in India and hell is called Narak. Those who do good deeds go to Swarg and those who do bad deeds go to Narak. Jaisi karni waisi bharni, they say in India. This means as you act thus you reap the result. Punishment for bad actions and reward for good actions.
Concept of Prophethood has been the one that has been significantly obliterated in India. But even then there are very clear evidences of the same. Narad Muni is one demi-god in Indian mythology who is a messenger from gods above to the people on the world.
Obliteration of Prophethood is because of excess in religious matters.
This type of excess is quite common on part of humanity.
Uzair (AS) was a Prophet Jewish people made him son of God.
Jesus Christ (AS) was a messenger but Christians made him son of God. Or even God, or one of the three Gods.
Similarly in India the number of gods is huge.
This can not be the truth, God can only be One True God.
This over exaltation of pious personalities is quite common in India.
Just in front of our eyes Sai Baba has joined the rank of gods.
So has Sathya Sai Baba.
For some time a holy man Jahar Pir in north India has joined the same rank.
Allah (SWT) does not like it. He dislikes it to the highest extent when others are exalted to His level.
Pious people should kept at their own levels. They might be better than us but they do remain slaves of Allah (SWT).
A Hindu teacher of mine explained it very clearly when I visited him after decades. This teacher has become a Swami. He said that suppose there is a country then there can be only one Prime Minister. Deputy Prime Ministers can be more than one but Prime Minister can only be one. Similarly President can only be one. Vice Presidents can be more than one. Clearly true God can only be One.
And if there is One God then religion given by Him has to be the true religion.