The same purpose as the grain of sand on the beach under the one on top of it, on top of the one below it. The grain is where it is after it found a solid found

The same purpose as the grain of sand on the beach under the one on top of it, on top of the one below it. The grain is where it is after it found a solid foundation for it to rest on. The grain on top of it in turn rests on the ones below, and so forth - it is grains of sand all the way down and up.