Rambam

Many philosophers have talked about the concept that everything in this world has a purpose. For example, upon observation of a hammer, one can see that it is obviously for banging. All tools must have a job or the craftsman wouldn't have made it. The Rambam takes this further and helps us understand why G-d created the world with so many types of plants and animals. The answer is that if you knew the different properties of everything you would understand why for example, though a plant is poisonous if you eat it, but when you use it as a cream it can heal you.
The Rambam asks a further question: why did G-d create man? One might say that man was created to eat or procreate. However, animals eat and procreate as well! Therefore, we must look at the difference between man and all other creations and see that the only real difference between man and animal is intelligence, specifically in the realms of dibbur and communication. This tells us that our whole reason for existence is to use our wisdom and refine ourselves to do more than the animals do.
The Rambam asks, if our existence is only because we have intelligence, why are some people “stupid”? It’s a good question because if a fly cannot do its job of flying in the wild it gets destroyed very quickly. People, on the other hand, can live very good lives and still not use any refined wisdom. He answers that the role of the non wise is for them to serve the wise. This means that if men would all do nothing but learn and study and grow spiritually then we would all starve to death. The world would have no roads, farms, or government. Therefore, G-d had to create some men with higher levels of wisdom than others.
This leads to one last question. If the intelligent, wise, spiritual people are supposed to be served by the non intelligent, wise, spiritual people then why are there some rich, happy, never worked a day in their lives type people that do not have an intelligent, wise, spiritual bone in their body? This can be answered with the following mashal: a Rabbi walks in the dessert until he can not walk anymore unless he gets a drink and some shade. He sees a mansion nearby with a vineyard. He musters up his last bit of energy and makes it to the shade of a massive wall. The owner, a wealthy lowlife, sees the Rabbi and gives him a drink from the grapevines. The Rabbi survived the episode only because G-d allowed an ignorant and non spiritual person to obtain a wealth large enough for him to have a massive wall and a vineyard all at exactly when it was needed.
We can now understand that every creation has a role in this world. We must use our ability to be higher than animals to serve Hashem or we are no better then a fly without wings.