Candide by Voltaire, Chapter 18

[Candide] asked whether the people of that country [El Dorado] had any religion.

The old man reddened a little at this question.

"Can you doubt it?" said he, "do you take us for wretches lost to all sense of gratitude?"

Cacambo asked in a respectful manner what was the established religion of El Dorado. The old man blushed again and said, "Can there be two religions, then? Ours, I apprehend, is the religion of the whole world; we worship God from morning till night."

"Do you worship but one God?, said Cacambo, who still acted as the interpreter of Candide's doubts.

"Certainly," said the old man; "there are not two, nor three, nor four Gods. I must confess the people of your world ask very extraordinary questions."

However, Candide could not refrain from making many more enquiries of the old man; he wanted to know in what manner they prayed to God in El Dorado.

"We do not pray to Him at all," said the revered sage; "we have nothing to ask of Him, He has given us all we want, and we give Him thanks incessantly." [As El Dorado is super rich and devoid of disease, hunger or poverty]

Candide had a curiosity to see some of their priests, and desired Cacambo to ask the old man where they were. At which he smiling said, "My friends, we are all of us priests; the King and all the heads of families sing solemn hymns and thanksgiving every morning, accompanied by five or six thousand musicians."

"What!" said Cacambo, "have you no monks among you to dispute, to govern, to intrigue, and to burn people who are not of the same opinion with themselves?"

"Do you take us for fools?" said the old man. "Here we are all of one opinion, and know not what you mean by your monks."

In my view, El Dorado is Voltaire's vision of what a utopia is, and surprisingly it reads a lot like how I view the religion of Islam: It is ridiculous to say they is more than one God. All people on Earth acknowledge this one God and thank and pray and ask of Him alike, hence there is one essential religion, and no-one is a priest over another as the knowledge is open to all of us to become our own guides.