Do you think Picasso painted his many masterpieces using only his fingers as his tools? No way! He painted precision shapes and did exquisite shading with patience, creativity and the assistance of his brushes. Once you've applied your makeup, you probably don't want to look in the mirror and mistake your face for a painting by Picasso. Remember, you are indeed a beautiful work of art and applying proper makeup is also a form of art.
The proper tools will allow you to achieve a flawless look without all the stress. Whether you want to draw the finest eye line, find a natural looking way to wear your lipstick or just want to be able to apply your makeup faster - brushes will give you that freedom. There are simply things you cannot do and effects you will never achieve without a brush.
One main reason to use makeup brushes is that they give you more control. Despite the type of product you are working with, a brush will always give you the ability to manipulate and maneuver your makeup. In this same regard, makeup brushes offer you better accuracy in your application.
The size and shape of your brush should typically relate to the desired effect you want to create and also the area to be worked on. The smaller the area you are working on, the smaller your brush should be. Conversely, the larger the area, the larger the brush needed. This is just a general guideline and not a law, of course.
Working with brushes usually means better hygiene. Fingers can be very useful and do make wonderful tools, but think about where they've been. Even when you wash your hands before you do your makeup, how many things do you have to touch before your fingers even make it to your face? Aside from placing excess oil, dirt and bacteria onto the skin, fingers also deposit those things into your makeup if you are dipping them directly in the product. Using a clean brush to begin, and swiping the brush on an alcohol pad/wipe between dips will help to reduce unsanitary makeup and lessen the likeliness of breakouts.
If you wear a similar makeup style from day to day, you will be amazed at how much time you will save by using brushes instead of other methods. Once you learn which colors you need to apply with which brushes and to the appropriate areas of the face, you can practically turn the auto-pilot on and as it all becomes second nature. Brushes give you the ability for superior blending, which is one of most important things when it comes to makeup. You also get more visibility, as brushes typically have long handles which let you put more space between your hand and your face.
Most makeup artists probably have a shoebox full of brushes. The average person, and beginners, can do just fine with only a few. You can look forward to an in-depth review on brush types and their functions to come.
Art, makeup, beauty... they are all so closely related; all are open to interpretation. The most important thing to learn/accept/know is that you are beautiful, and you are someone's masterpiece.

