If thy whole body therefore be full of light, having no part dark, the whole shall be full of light, as when the bright shining of a candle doth give thee light. The Lord here completes his allegory, still preserving the same images, with a sketch of the condition of a holy and humble man of heart, who with a "single eye," that is, honestly, trustfully, lovingly, has looked upon the sign and believed.
Godet's comment on this hard and mystic saying of the Blessed is very beautiful: "When, through the fact of the clearness of thine eye, thy whole body shall be penetrated with light, without there being in thee the least trace of darkness, then the phenomenon which will be wrought in thee will resemble what takes place on thy body when it is placed in the rays of a luminous focus.
Jesus means that from the inward part of a perfectly sanctified man there rays forth a splendor which glorifies the external man, as when he is shone upon from without. It is glory as the result of holiness.
The phenomenon described here by Jesus is no other than that which was realized in himself on the occasion of his transfiguration, and which he now applies to all believers." There is little doubt that this teaching had been spoken by the Master on one, if not on more than one, previous occasion.
In St. Matthew's report, in almost identical language (Matthew 5:15 and Matthew 6:22), the immediate application was different, and the reference of the lamp put in a prominent place was not to the Resurrection.