MATTHEW 6:22-24
Jesus is speaking of spiritual vision. If we keep our attention (eye) single upon Jesus, the Word, then all that we will be filled with is the light of His Word (John 1:1-14; Psalm 119:105). The key to victory is this singleness of purpose (Philippians3:13). The strength of the laser lies in the fact that all of the light is concentrated on one single point. The strength of the Christian lies in how single his or her vision is upon Jesus, "the author and finisher of our faith." (Hebrews 12:1-3)
We may have God and riches, but we can only serve one of them. In Matthew 6:24, the Lord stresses this by saying that we cannot serve two masters. Why? Because we do not have the capability of faithfully serving both of them. We will cleave to one more than the other. We cannot serve both with all of our heart. We just don't have the capacity to do our best in two areas at the same time. God wants singleness of vision, singleness of purpose. He wants us to serve Him with all of our heart.
We can still make a living without always thinking about money. Where will it come from? How will we get more of it? Jesus says that He will supply all of your need when we seek first the Kingdom of God. All of these other things (food and clothing etc.) will be added unto us. If we will simply put God and His Kingdom first in every area of our lives, He will add to us all the wealth that we need. It's when we covet after money that we "pierce ourselves through with many sorrows" (1 Timothy 6:10).
Put God to the test. Put Him first in every area of your life and see if He won't provide all the other things for you.