Why Allah did not permit the Sun to overtake the Moon?

Qur'an 36:38 "The sun keeps revolving in its orbit at the dispensation of the All-Knowing. And the Moon, We have measured for her mansions till she returns like dried date stalks. It is not permitted for the Sun to overtake the Moon, nor can the Night outstrip the Day. Each (just) swims along, floating in (its own) orbit as a Sign as in a race. And we made similar vessels [chariots] for them to ride. But we could have drowned them if we pleased."