In Matthew 6:23-24, Jesus turns from the comparative durability of the two treasures to the comparative benefit to be derived from two conditions. The contrast now is between a blind person and a sighted person, and so between the light and darkness in which they respectively live. The eye is the lamp of the body. This is not literal, of course, as if the eye were a kind of window letting light into the body, but it is a readily intelligible figure of speech. Almost everything the body does depends on our ability to see. We need to see in order to run, jump, drive a car, cross the road, cook, embroider, paint. The eye, as it were, ‘illuminates’ what the body does through its hands and feet. True, blind people often cope wonderfully, learn to do many things without eyes, and develop their other faculties to compensate for their lack of sight. Yet the principle holds good: a sighted person walks in the light, while a blind person is in darkness. And the great difference between the light and the darkness of the body is due to this small but intricate organ, the eye. If your eye is sound, your whole body will be full of light; but if your eye is not sound, your whole body will be full of darkness. In total blindness the darkness is complete.

All this is factual description. But it is also metaphorical. Not infrequently in Scripture the ‘eye’ is equivalent to the ‘heart’. That is, to ‘set the heart’ and to ‘fix the eye’ on something are synonyms. One example may be enough, from Psalm 119. In verse 10 the psalmist writes: ‘With my whole heart I seek thee; let me not wander from thy commandments,’ and in verse 19, ‘I have fixed my eyes on all thy commandments.’ Similarly, here in the Sermon on the Mount. Jesus passes from the importance of having our heart in the right place to the importance of having our eye sound and healthy.

The argument seems to go like this: just as our eye affects our whole body, so our ambition (where we fix our eyes and heart) affect our whole life. Just as a seeing eye gives light to the body, so a noble and single-minded ambition to serve God and man adds meaning to life and throws light on everything we do. Again, just as blindness leads to darkness, also an ignoble and selfish ambition (e.g. to lay up treasure for ourselves on earth) plunges us into moral darkness. It makes us intolerant, inhuman, ruthless and deprives life of all ultimate significance.

It is all a question of vision. If we have physical vision, we can see what we are doing and where we are going. So too if we have spiritual vision, if our spiritual perspective is correctly adjusted, then our life is filled with purpose and drive. But if our vision becomes clouded by the false gods of materialism, and we lose our sense of values, then our whole life is in darkness and we cannot see where we are going. Perhaps the emphasis lies even more strongly than I have so far suggested on the loss of vision caused by covetousness, because according to the biblical thought an ‘evil eye’ is a niggardly, miserly spirit, and a ‘sound’ one is generous. At all events Jesus adds this new reason for laying up treasure in heaven. The first was its greater durability; the second the resulting benefit now on earth of such a vision.