But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God.
Matthew 4:4 (KJV)
We do not live by bread alone because we are not only physical beings. Just as our physical body requires physical food, so too our born again spirit—the innermost part of who we are—requires spiritual food in order for us to reach our full potential in Christ. We are being spiritually fed anytime we receive the Word of God; anytime we consider it, meditate on it, and take it into our hearts. The more that our spirit is fed, the stronger our inner person becomes. And when our spirit is strong, our ability to be victorious over the flesh increases.