No man, when he hath lighted a candle, putteth it in a secret place, neither under a bushel, but on a candlestick, that they which come in may see the light. The Lord continues his reply to those who asked him to support his claims by a visible sign from heaven, "Do not think for a moment that the sign I speak about, and which was prefigured in the story of the Prophet Jonah, will be an obscure or secret thing. No man lights a lamp to hide: so will it be with that sign which will be given to you." Jesus was speaking all the while of the mighty sign of his resurrection.
The light of the body is the eye: therefore when thine eye is single, thy whole body also is full of light; but when thine eye is evil, thy body also is full of darkness. Take heed therefore that the light which is in thee be not darkness. He goes on, though, with his solemn warning words. Plainly visible though the sign would be—shining bright as a lighted lamp set on high—still it, too, was possible to miss seeing it. If the eye, the organ of the body which perceives the light, be sound and healthy, then the illumination given by the lamp is seen, and the whole body, so to speak, is full of light; but if the eye was diseased, purblind, no bright shining light would be seen—the body then would be full of darkness. The word rendered "single" denotes the eye in its natural healthy state; that translated "evil" speaks of the eye as diseased, as incapable of perceiving the rays of light. The imagery to those Orientals, accustomed to parable and allegory in the stories and poems they had listened to from their childhood, was easily translated into the language of everyday life. If they gave way to passion, jealousy, prejudice, impurity, lawlessness in its hundred forms, then for them the spiritual eye of the soul would become diseased, and therefore incapable of rightly discerning any heavenly sign. It was this danger that the Master was pointing out to the crowd. "Ah!" he seems to say, "you ask a heavenly sign which will substantiate my lofty claims; that sign, in a grander and more stately form than ever you have dreamed of, shall, indeed, be given you. Have no fear on that score; rather dread that blindness, the punishment of a hard and evil heart, will come upon you, and render you incapable of seeing the sign you ask for, and which I mean to give you." He was speaking still of his resurrection. Alas, for them! the blindness of which he warned them was the unhappy lot, we know, of very many of those listening then.