The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.
Note 39 at Mt 6:22: Jesus was speaking of spiritual vision. If we keep our attention (eye) single upon Jesus, the Word (Joh 1:1 and 14), then all that we will be filled with is the light of His Word (Ps 119:105). The key to victory is this singleness of purpose (Php 3:13). The strength of the laser lies in the fact that all of the light is concentrated on one single point. Likewise, the strength of Christians lies in how single our vision is upon Jesus, the Author and Finisher of our faith (Heb 12:1-3).