Here "heavens" refers to the sky, and is spoken of as if it were a building in which God stores the rain. See how you translated a similar phrase in [2 Chronicles 6:26](../06/26.md). Alternate translation: "Suppose that I do not allow the rain to fall from the skies" (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here "send disease" represents causing diseases. Alternate translation: "if I cause my people to have diseases" (See: [[rc://en/ta/man/jit/figs-metaphor]])