The existance of an Organization is required because Transaction costs of the market are often too high to run any operation of decent complexity directly using the free market.
Imagine a scenario where an entrepreneur has access to an Ideal Market - whatever they wanted to get done is available on the market for the right price - instantaneously and exactly as required. This is an ideal scenario - an ideal market. Reality is not different though, there are many transaction costs in an imperfect market. Read more.
An organization can reduce the number of transactions on the market by working internally to produce the same results.