Normally "the fruit of his labor" simply refers to the results of his labor. In this case it refers to the things the wicked man had stolen. Alternate translation: "the things he had worked to get" or "the things he had stolen" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-explicit]])
Here "to swallow" the fruit of his labor represents enjoying the things he had stolen. Alternate translation: "will not be able to enjoy them" (See: [[rc://en/ta/man/jit/figs-metaphor]])