This is an idiom that means he will begin to act. It does not mean that he was sitting or lying down when he said these words. (See: [[rc://en/ta/man/jit/idiom]])
Jewish people sometimes avoided saying the word "God" and used the word "heaven" instead. Alternate translation: "I have sinned against God" (See: [[rc://en/ta/man/jit/figs-metonymy]])