Good question my dear friend.
I pray my guru and god to give me the power to give the correct answer for this question.
My dear friend, I too heard that other religion people saying that in Hindu religion, many gods and goddesses are there. If we observe Islam they have many prophets even Allah is also a prophet not GOD. In Islam they are different casts are there Example:-Sufis, Sunnis, Judas Etc., Almighty is the only one. And about Christians Jesus Christ, he him self told that he is the son of god. i.e., he is a prophet. And Christians are having many sub-casts are there like Example :- Romans , Catholics, Cists, etc., but all the sub casts in Islam and Christians are leading towards peaceful life in society and towards almighty.
In all religions of the world the maximum number of people are missing the right preaches form wise people. The religions are formed to survive humanity in different areas with different kinds of beliefs about god to reach god. All the religions are the different paths to reach god. But still because of not having or not developing proper educare they are producing such type of haste and insulting talk about holy religions.
Not only Hinduism but all the human religions living on the earth are following the GURU siddhanta.
From the ancient days of human formation, human is a student to nature and he is learning every thing from nature. Human is the student of nature. Jesus Christ is the GURU for Christians and Allah is the GURU for Muslims. And for Hindus DATTATREYA or GURUDATTA is the GURU for all humanity.
But RELIGION is just like climbing through a stairs we can start your worship as your likes but self realization will transit you to a new step which is will nearer to the god. so, god did'nt change his form, but we can reach him with infinite form
And about Hindu gods.
Almighty god is only one. He is shapeless, he spread him self to all the universe and kept his god powers in Shakti. Shakti created 2 sons Shiva and Vishnu. And she distributed her god powers to them both.
Lord Shiva Rules the world with the help of Lord Vishnu. Lord Shiva is called the destroyer
Lord Vishnu is the decision maker. Lord Vishnu makes decision about life and happenings about the beings on the earth.
Then Vishnu created Brahma they both give him the duty of creation.
At a certain occasion the three GODS Bramha, Vishnu and Shiva merged their shapes in the form of DATTATREYA. And he is called as GURU his is having the power of god again.
He is the form of GOD, preacher every thing. Even the forms of Vishnu, Shiva are also served the culture GURU.
My conclusion is the culture of HINDUISM is Serving GURU. The one and only guru.
He is called as GURUDATTA or DATTATREYA.
ADIPRASHAKTI is the guru for LORD SHIVA --> Vishnu--> Bramha --> etc., its continuing