The meaning of Ma Shi's poem "There is as much sand as snow in the desert".

Ma Shi's twenty-three deserts are as sand as snow, the endless desert is separated by a layer of snow, and the moon in Yanshan is like a silver hook. When can I take the luxurious horse faucet and gallop on the battlefield in autumn? The poet compares himself to a horse, which is obviously a feeling that he is incompetent and the hero is useless.