Religion

God: In the world of One Piece it is unknown whether such entity exists, yet there is many religious references scattered across the series. In Skypiea, this title refers to the ruling body of sky islands, instead of any kings or other form of government, God is usually looked at as the ruler. This person however is not a real God but a physical being who is not all powerful and not perfect. Smoking God was the oldest known God 400 years ago, and Gan Fall was the previous God 6 years ago, before Eneru took over. Eneru took this title seriously, believing to be an all-powerful God only to be beaten up by Luffy. After Eneru was gone, Gan Fall reclaimed the title.

Does God exist in One Piece?
Sanji has made many references of a possible God, even once asking Zoro of his believes, though Zoro did not answer because he doesn't believe in a God. Again after defeating Jyabura, Sanji mentioned God.

However, Conis questions if whether or not God exists, she then shouts out Help us, God!!.

Bartholomew Kuma has a Bible in his hands and always carries it with him. Mihawk also has weapons modeled after crucifixes, so the Shichibukai might be a Holy organization, considering the fact that the privateers they are modeled after were also a very Holy people.

Trivia

 * In a 1993 Oda's oneshot called God's Gift for the Future, previous to One Piece, Gods appears as a comical old man who isn't omnipotent at all although he's supposed to be the real thing.