In the beginning there was God. He was bored, being all alone, so he decided to create the physical world, and populate it with all sorts of beings, among them, humans. He gave the humans one commandment - though he knew that the humans will disobey. When humans disobeyed, God became angry (why? didn’t he know that it will happen?) and cursed the whole creation (all those zillions of galaxies), creating a miserable existence. Millennia passed.
All of a sudden God decided that the experiment was a failure, and decided to ditch it. He sent a deluge and drowned all the humans and animals (what about the fish?) - while he kept a few samples to restart the whole shebang. Hmmm, didn’t he know that it will fail again? Millennia passed, and people were as they always have been, some good, some bad.
So God decided to suffer a split personality, and went down to the humans in a semi-human form. He knew that he will be crucified but he needed that to be able to pardon the transgressions of the humans. Just like any other pagan god, he needed a sacrifice, but he would not have been happy with animal sacrifice, or even human sacrifice. No sir! He had to sacrifice himself. What a novel idea! Of course he botched that, too. He was unable to kill himself, so he spent a few days in some unspecified place, called hell, and then ascended into heaven, where he could sit on his own right hand side. How can you sit next to yourself is a “mystery”.
Millennia still keep passing. People are just as they have always been, some good, some bad. Presumably, God still ponders, how could he make a better world, where everyone could share the bliss emanating from him. Well, when he finds a good method, I am sure we shall all find out about it. Until then we can hope that he meant what he said about “no more Deluge”. Of course that does not exclude some other methods. A huge meteor might strike the Earth, or the Sun can go nova, or maybe an ice-age will restart the failed experiment.
Life is a “mystery”.