Start from here:
Back when people blindly believed in religion, God and every petty ritual that came in the package of religion people were most probably more tolerant to each other’s faith than those who try to convince everyone that they are the spokesperson of God on earth. That God is of course different for different religions… they don’t believe that one, single power is capable of taking care of the entire universe’s positive powers.
Now, back then sages like Kabir, Guru Nanak had followers from all religions, who knew that there was but one God and everyone followed that same God. Now, after all these modern studies and actual enlightenment against superstitions we are diving back to middle age, trying to paint God in different colours!