In Matthew 6:22-23 (NET) Jesus teaches the following, 
“The eye is the lamp of the body. If then your eye is healthy, your whole body will be full of light. But if your eye is diseased, your whole body will be full of darkness. If then the light in you is darkness, how great is the darkness!”
Notice that he is highlighting two realities:  your eye and light.  Here are some thoughts to consider.
Your eye is the lamp of your body in that it guides your bodily movements.  So I think we could say that Jesus is referring to what guides all you do — your will.  
Now just as your eyes need and use LIGHT in determining where to go and what to do, so your day to day decisions — your will — needs a reason to act, that is, it needs a MOTIVE. 
Hence, your motives are, in effect, the light by which you exercise your will.
So if your will is healthy, that is, committed to helping others come what may, then your motivation will give you light and your whole body — all your activities — will be full of light.
But if your will is divided, that is, committed only when it’s expedient, then your will is diseased, and the light — your motivation — is darkness.  All your activities will be full of darkness.

Ver todos los episodios