Colossians 3:16 (NKJV)
Generally speaking, you cannot have more going out of something than you have coming in. This is true financially and it has been said that if your outgo exceeds your income, then your upkeep will be your downfall. This principle is true physically, if you expend more energy and effort in activities than you take in nourishment you will become weak. Another example would be with a car, you can only drive your car as long as you have gasoline in the gas tank. This same principle is also true spiritually, if we are giving out more than we are taking in we will have trouble.
Colossians 3:16 tells us to let the Word dwell in us richly, but this requires action on our part, it is not something that happens automatically. We first have to take in the Word of God so that it can dwell in us. The second part of the verse shows the result of our having a rich supply of the Word of God in us, we can teach and encourage each other and we will sing with grace in our own heart. If our supply of the Word is low it will have an effect on our ability to help others and maintaining a healthy spiritual level for ourselves. Without a continual supply of God's Word we become weak spiritually.
Some people just think about how important it is for those who are teaching and encouraging others to have a supply of God's Word without realizing the problems each of us will have in our own spiritual life if we do not let the Word dwell in us richly. Trying to live the life God intends for us to live day after day without continual input from God's Word will create a deficit due to more output than input. We have to know the Word, speak the Word, meditate on the Word, and do the Word to keep ourselves spiritually fit and to help others. We need to have an abundant supply of God's Word in us.