why the earth rotating

From another view,it maybe involves the origin of the world even universe. The science can only explain the world to a certain level, but for the ultimate answer, it's the problem of philosophy.

My understanding is that the earth rotates because it is tilted on an axis and is caught in the gravitational pull of the Sun. Seasons present themselves as the tilting of the Earth on its axis moves the Northern or Southern Hemisphere either closer to or further away from the Sun. The rotation of the earth also provides us with gravity (centrifugal force). If it were to stop spinning, everything on Earth not bolted down would pretty much float off into space..... We have 24hours in a day because the Earth takes that amount of time to complete one rotation. We have 365 days in a year because it takes the Earth 365 and one quarter days to orbit the Sun (hence a leap year every four years)