Matthew only. Ye are the light of the world. After speaking of the moral tone that the disciples were to give to the world, in contrast to sin in its corrupting power, Christ refers to them as enlightening, in contrast to sin as darkness and ignorance.
Our Lord further naturally exchanges the term "the earth" (which from its strong materialism had suited the figure of the salt) for "the world"—a phrase which must, indeed, as regards the disciples, be limited to this earth, but as regards the light, need not be limited to less than the solar system.
In other words, the simple reason why he exchanges "earth" for "world" is that they are respectively the best suited to the figure employed. Notice that Christ never applies the former figure, of salt, to himself; but the latter, of light, once or twice, especially John 8:12, where, since he is speaking of himself, and not of others, he adds the thought of life being connected with light, a city, etc.
; literally, a city cannot be hid when set on a mountain. It seems at first slightly awkward to introduce the figure of a city between those of the sun and the lamp, both these having to do with light.
The reason is that the city is not considered as such, but only as an object which can be teen, and which cannot ( οὐ δύναται, emphatic) from its physical conditions avoid being seen. There is a true gradation in the thought of influence.
The sun must be seen by all; the city, by the whole neighbourhood; the lamp, by the family. Our Lord comes from the general to the particular; from what is almost theory, at best a matter of hope and faith, to hard fact and practice.
The influence you are to have—if it is to be for the whole world, as indeed it is, must be felt in the neighbourhood in which you live, and a fortiori in the immediate circle of your own home. Conjectures have been made whether any one city can reasonably be mentioned as being in sight, and so having suggested this image to our Lord.
If the exact spot where he was then sitting were itself certain, such conjectures might be worth considering. But, in fact, so many "cities" in Palestine were set on hills that the inquiry seems vain.
Safed, some twelve miles north-west of Capernaum, the view from which extends to Tiberias, has been accepted by many, but evidence is lacking for it having been a city at that time. Tabor, at the south-west of the lake, has also been thought of, and at all events seems to have been then a fortified town.
The view from it is even more extensive than from Safed.