David said in his heart

Here "his heart" is a metonym that means to himself. Alternate translation: "David thought to himself" (See: rc://en/ta/man/jit/figs-synecdoche)

escape out of his hand

The word "hand" is a synecdoche for the person. Alternate translation: "escape from him" (See: rc://en/ta/man/jit/figs-synecdoche)