Because it is written (Shemoth 23:5) "Unload shall you unload (his animal) with him," I might think that you should unload for this one, too; it is, therefore, written "and you shall not hearken to him."
Because it is written (Vayikra 19:16) "And you shall not abide the (spilling of the) blood of your neighbor," I might think that the same applied to this one, too; it is, therefore, written "and your eye should not look mercifully upon him."
"and you shall not pity": You shall not argue in his defense.