According to Genesis 1:14, God created the Moon and the Sun for signs, seasons, days, and years. So the Moon helps us divide our years into months. If you didn't have a calendar, the Moon could also tell you how far into the month you are at a given day.
In verse 16 of that same chapter, it says the Moon was designed to “rule the night”. And rule the night it does. Appearing to look so much larger than any other object in the night sky, it outshines everything in the sky. Furthermore, it has a tendency to wash out most other astronomical objects, making them more difficult to see. This is most evident when the moon is near its full phase, as it is over 2500 brighter than Venus, the second brightest object in the sky.
The Moon also plays a crucial role in controlling our oceans, so the marine life survives, and oxygen production continues. It has also been determined, that the Moon helps to stabilize our planet.