The Scythe is one of the attributes of personified Death. In early renderings, the Reaper is shown holding arrows, darts, spears or crossbows. These are the weapons he uses to strike down his victim.
Over time, the scythe came to replace these other instruments of death. A scythe was a tool used to reap, or cut, grain or grass. Bringing this imagery to death was a natural extension of an agrarian society in which harvesting, done in the fall, represented the death of another year. Just as we harvest our crops, so does death harvest souls for their journey into the afterlife.