The lamp of the body is the eye. If therefore your eye is good, the whole body will be full
of light. But if your eye is bad, your whole body will be full of darkness.
Have you ever observed how an icicle is formed? It begins with a single drip that freezes. Then drip after drip runs down, only to freeze at the tip or one side. If the water was clean and clear, the icicle will be equally dear. But if the water was dirty, then the ice formation can itself look only cloudy.
The formation of our character is very similar. Whatever we permit to influence us will have its effect on our personality. All that takes hold on our heart will also stamp our character and our life.
If what occupies our thoughts corresponds to God's standards, the formation of our character will be positive, and our heart and mind will be filled with bright, pleasant light. But impure, sinister thoughts also inevitably exert their influence on our character. It is therefore important for us to examine time and again what thoughts and feelings we permit to enter and dwell in our heart.
In this connection the Lord Jesus spoke of a “single” or “good” eye. In the figurative sense, single-minded is what is meant. This signifies the clear and definite orientation of a heart that loves God and wishes to serve Him in all things. Then we naturally endeavour to keep our thoughts, feelings and motives clear, pure and good in the strength which He gives us.