Colossians 3:16 (NKJV)
Different types of cars use different types of gasoline and some vehicles use diesel fuel. When you want to put something in your car to make it run, and run properly, you need to have the right kind of fuel. The biggest difference in fuel is between gasoline and diesel, but there are also different octane ratings for gasoline. Some cars run better on one type of fuel than they do another, and for some cars there are recommended octane ratings that the gasoline used needs to have. If you put the wrong type of fuel in your car it can cause some problems, but if you get the right fuel you can fill up your tank and drive for a long distance.
If you just drive your vehicle without refueling eventually you will run out of gas and come to a stop. In a similar way, if we try to live our lives without keeping ourselves full of God's Word then we will eventually come to a place where we can no longer function the way that we should. Or, if you fill your vehicle with the wrong type of fuel, you may move forward but the vehicle will not operate as efficiently as it should. The same is true spiritually, if we fill ourselves with things that are contrary to God's Word we can still go on living our lives, but we will do it less effectively than we should.
Just like we can take our vehicle to a place to get the necessary fuel for it, we go to the Bible to fill ourselves up spiritually. God's Word gives us what we need to live our life and keep on going. Some people say that prayer is the necessary fuel for the Christian life or that singing, praise, and worship are the key. But, while all of those things are great, if they are not based on the Bible they will not do anyone any good. As Colossians 3:16 tells us, we need to let the Word dwell in us richly, we need to fill up on God's Word. God's Word is the fuel we need for our spiritual life and we need to fill ourselves with it.