When was the last time you asked a question with childlike wonder, like "Why is the sky blue?" If it's been a while, let's try one now.
Why did God create a world with clouds?
Scientifically, we could answer that clouds consist of water that has evaporated, then condensed into vapor. When these vapor particles combine and become heavy enough, they will fall as rain. As described by meteorologist, Jeff Pardo, clouds "help regulate the earth's energy balance, by reflecting and scattering solar radiation or absorbing the earth's radiated infrared energy. Clouds maintain the earth's atmospheric stability because clouds form when air rises and cools. When a blob of air goes up into an area of less pressure, it cools. When it reaches its dew point temperature, the rising parcel is no longer unsaturated. Water begins to condense, and it then rains."
This is why the Talmud states that God never withholds clouds from the world -- they are required constantly for the world's existence. (Taanit 3b)
But there are deeper mystical lessons contained within the clouds. The verse states "God covers the heavens with clouds and prepares rain for the earth" (Psalms147:8).
The onset of heavy, dark clouds may appear somewhat menacing, but it is really nothing of the sort. God brings the clouds and fills them with rainwater, bringing tremendous blessing to the world. The lesson is clear. God often send us worries and troubles but in the end we come to understand that the purpose of the ordeals was to carry us to great achievements.
In a deeper vein, Kabbalists suggest that there are times when God brings clouds to block the sunlight for ecological purposes. Similarly, there are times when God presents blockades to spiritual success for certain purposes. If a person stares directly into the sun, his eyesight is temporarily impaired, and prolonged exposure would lead to vision damage. This is why we cannot tolerate staring into the sun.
We experience this in the spiritual realm as well. There are times when jumping to great spiritual heights too quickly is damaging to our growth. One who takes on too much too soon can easily burn out and, in the end, regress.
Stable growth needs to happen gradually. Taking on too much, too fast, most often doesn't last. This is one of the reasons God redeemed the Jewish people from Egypt in stages; releasing oneself from an idolatrous Egyptian culture cannot be done overnight.
Spiritual growth requires patience and consistency. Remember, it doesn't matter how high up you are on the spiritual ladder, as long as you are moving up.
Perhaps this is why God blocks the sun with clouds. Ultimately the clouds purpose it to produce the blessing of rain; in spiritual terms the clouds remind us to aim for permanent, steady growth, one step at a time.
Clouds act as a type of barrier, letting us know that there are levels that are presently beyond us and we shouldn't leap to heights we're not yet ready for. But when we do climb the ladder and finally reach the clouds, we see that they have no strong substance to them. You can fly right through them! Clouds are a mirage, they are not real obstacles.
The message is clear. Once we start to grow spiritually and embark on the path toward heaven, we should not be intimidated by the obstacles, the clouds that lie before us. They are an only an illusion. Just keep soaring and you'll pass right through them.