Originally, the sun and the earth were born from dust floating in space, spinning. The earth is still spinning because it still retains the rotation it had at that time.
The sun, the earth, and most of the planets in our solar system were born from the same direction of rotation of cosmic dust. Thus, the sun, earth, and most of the planets are all spinning in the same direction, even though they are very far apart. This is evidence that they were born from the same rotation.