Expositor's Bible Commentary Commentary Luke 11:36

"If therefore thy whole body be full of light, having no part dark, it shall be wholly full of light, as when the lamp with its bright shining doth give thee light." — Luke 11:36 (ASV)

The body is only completely lighted when a lamp shines on it from the outside (cf. Ephesians 5:13–14a). That is, full illumination only comes when one is willing to receive light from the lamp of God’s truth.