Where Did the Moon Come from?

The Moon is four times smaller than the Earth, orbits the Earth in a very circular and tilted manner, and is of great importance to life on Earth. Twelve astronauts have walked on it. 

There have been several different secular explanations for the origin of the Moon, see time 0:39–9:41 in PhD Christian Scientist Exposes the HUGE Faults in Cosmic Evolution. The latest and most popular one is the Giant-impact hypothesis. According to this theory, the Moon is believed to have formed about 4.5 billion years ago, not long after the Earth was formed. The Moon then formed from the debris left over from a giant impact between Earth and a Mars-sized body called Theia. (The details haven't been clarified yet). There are problems with this explanation:

• Evidence of recent volcanic activity on the Moon is inconsistent with a high age because the Moon should have cooled by then.
• The Moon now moves 1.5 inches (3.8 cm) away from Earth each year.
  Going back at most 1.4 billion years, the Moon will touch the Earth
  which of course isn't possible, but can be seen as an upper limit, see
  time 48:07–49:48 in "Astronomy Reveals Creation" with Dr. Jason Lisle.
  
  The effect is due to the tidal waves as a disc brake on the Earth, slowing its rotation. However, the momentum of movement must be conserved, which is transferred to the Moon, giving it faster rotation and a wider orbit. Because the tides were larger when the Moon was closer to Earth due to the higher gravitational pull, the Moon used to move farther away per year than it does today. Watch The Moon is Drifting Away, Moon recession, Moon Recession, and The moon's recession and age.
  
  But if the moon is uncomfortably close to the Earth, the Moon will be destroyed into pieces and the oceans of the Earth will boil away. This means the Moon must be much younger than 1.4 billion years. In a time view of 6000 years, the Moon has only moved a few hundred feet (a few kilometers), not enough to be noticed, see Evidence for a Young Earth. 
• This theory predicts that the Moon is made mostly of the Mars-sized body that is thought to have collided with the Earth, that the Earth and the Moon are made of different materials. But that isn't the case. The Earth and the Moon are actually like identical twins. The genetic code of planets is written in the isotopes of the elements. The Earth and the Moon have identical isotopes, meaning that the Earth and the Moon are made of the same materials.
• A good theory is relative simple (the fewer assumptions, the better the theory) and should make many correct and specific predictions. This theory has become more complex over time. More explanations have been added to make the theory hold together, see How the Moon was ACTUALLY Created. But this theory is the best they have that reject divine creation.

According to the Bible, the Moon was created on the fourth day of the creation week (Gen (1 Mos) 1:14–18), see The Biblical Creation and the Fall of Man. The Bible text says that one purpose is to be signs and for seasons, for days and years. It was placed in the sky by God, the Creator. There are reasons and purposes of the Moon:

• Nightlight. It's important for agriculture and for several parts in the world.
• Clock. You can determine the time on it.
• Calendar. Moon is so reliable. We can predict decades ahead when there will be a Lunar eclipse, because the Moon follows  the laws of nature, see What is Information?
• Total solar eclipse. A total solar eclipse causes the Moon to cover the entire Sun, providing beauty and the opportunity to better study the Sun's corona and other parts of the sky. This is possible because of the exact relationship between the size and distance from the Earth to the Moon and the Sun.
• Compass. You can see the direction with it.
• Without the Moon to slow the Earth's rotation, a day would only last 8–10 hours. A faster rotation would produce winds of 160–200 km/h.
• Stable seasons. Earth's axial tilt is approximately 23.5 degrees. This tilt causes seasonal changes in climate. The Moon helps the Earth's axis not change more and more often. If the tilt of the Earth's axis varied more strongly, life on Earth would be threatened. Without the Moon, the axis would have swung by as much as 90 degrees, causing extreme temperature variations.  
• Tide. The tides keep the oceans moving and healthy, and are responsible for half of the currents in the oceans. Half of our oxygen comes from marine plants that depend on the ocean currents. Without the Moon, the tides would have been less produced by the sun alone, and wouldn't have been able to constantly stir the ocean floor to ensure the necessary exchange of oxygen and nutrients. 

The Moon is a silent witness of creation (Rom 1:20). We can see the Creator's fingerprints in the Moon. The Moon is very unique compared with the other moons in our solar system, see the following times in 
The Origin & Purpose of the Moon (with Dr. Danny Faulkner):

•   1:08–  4:11: Why God made the Moon.
• 24:48–38:47: When and how were the craters formed?
• 38:55–42:00: How the Moon points to a young Earth.
• 42:15–47:11: Does the Moon rotate on itself?
• 47:40–51:59: The Solar eclipse, proof of design.
• 54:45–55:35: How the tides affect the oceans.
• 55:36–57:54: The Moon stabilizes the axial tilt. 

See also Evidence for Creation.