Sakaki began to be used in Shinto rituals because since ancient times people believed that gods sometimes choose to dwell in plants, and what's more, branches with pointed leaves (like the sakaki branch) are considered yorishiro (objects that represent the gods).
神事で使用される様になったのは、古来から、植物には神が宿り、特に先端がとがった枝先は神が降りる依り代とされた。