The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light. But if your eye is bad, your whole body will be full of darkness. If therefore the light that is in you is darkness, how great is that darkness! "No one can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. You cannot serve God and mammon [wealth or riches].

If our eyes do not see distinctly, we cannot walk without stumbling and falling. If we attempt to work for two different masters, we are sure to give satisfaction to neither. It is just the same with respect to our souls. We cannot serve Christ and the world at the same time. It is vain to attempt it. The thing cannot be done. The ark and Dagon will never stand together. God must be king over our hearts. His law, His will, His precepts must receive our first attention. Then, and not till then, everything in our inward man will fall into its right place. Unless our hearts are so ordered, everything will be in confusion. "Thy whole body shall be full of darkness."

J.C. Ryle