If you want a really good answer I suggest reading "The Mind Illuminated" by John Yates. Which mixes a spiritual practice with the actual science of the mind.
Meditation helps us grow by allowing us to cut out the negativity that fills our thoughts everyday.

By meditating on an object for a few minutes to a few hours, our brains become trained to stay calm, focused and become self reflective rather than irrationally reactive. Meditation practiced everyday can have profound effects in daily life. One will be able to stay on task by using the practice of focusing on doing one thing and doing it well. The mind will not be distracted by any outside forces. This will introduce a sense of accomplishment and overall well being to the meditator.

Meditation has been proven to (whether you believe in it or not) remove negative energies from you and feed positive detoxifying energy into your system. It is actually very important that one disconnects from everyday life and allows the brain to rest and rejuvenate. Meditation also teaches us discipline since it is not easy when you first start out and can take years and years of practice to even get past the 1st few stages.

With practice everyday for even a few minutes, you will be able to see the great benefits meditation can bring.