 First, for a function to be uniessential to an entity is for it to unify and organize all the parts of that individual into the whole that is the individual. For example, the time-telling function unifies and organizes all the tiny metal parts (hands, spring, gears, etc) into the whole which is the watch itself. Similarly, the sheltering function unifies and organizes all the planks of a wooden house into the entity that is the house itself.