Be the Light of the World

Matthew 5:14
13 You are the salt of the earth. But if the salt loses its savor, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled by men. 14 You are the light of the world. A city on a hill cannot be hidden. 15 Neither do people light a lamp and put it under a basket. Instead, they set it on a lamp stand, and it gives light to everyone in the house.…
Verse 14. - 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 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

This being the distinctive title which our Lord appropriates to Himself (Joh 8:12; 9:5; and see Joh 1:4, 9; 3:19; 12:35, 36)—a title expressly said to be unsuitable even to the highest of all the prophets (Joh 1:8)—it must be applied here by our Lord to His disciples only as they shine with His light upon the world, in virtue of His Spirit dwelling in them, and the same mind being in them which was also in Christ Jesus. Nor are Christians anywhere else so called. Nay, as if to avoid the august title which the Master has appropriated to Himself, Christians are said to "shine"—not as "lights," as our translators render it, but—"as luminaries in the world" (Php 2:15); and the Baptist is said to have been "the burning and shining"—not "light," as in our translation, but "lamp" of his day (Joh 5:35). Let it be observed, too, that while the two figures of salt and sunlight both express the same function of Christians—their blessed influence on their fellow men—they each set this forth under a different aspect. Salt operates internally, in the mass with which it comes in contact; the sunlight operates externally, irradiating all that it reaches. Hence Christians are warily styled "the salt of the earth"—with reference to the masses of mankind with whom they are expected to mix; but "the light of the world"—with reference to the vast and variegated surface which feels its fructifying and gladdening radiance. The same distinction is observable in the second pair of those seven parables which our Lord spoke from the Galilean Lake—that of the "mustard seed," which grew to be a great overshadowing tree, answering to the sunlight which invests the world, and that of the "leaven," which a woman took and, like the salt, hid in three measures of meal, till the whole was leavened (Mt 13:31-33)

Cross References
Proverbs 4:18
But the path of the righteous is like the light of dawn, That shines brighter and brighter until the full day.

John 8:12
Once again, Jesus spoke to the people and said, "I am the light of the world. Whoever follows Me will never walk in the darkness, but will have the light of life."

John 9:5
While I am in the world, I am the light of the world."

John 12:36
While you have the Light, believe in the Light, so that you may become sons of light." After Jesus had spoken these things, He went away and hid Himself from them.

Philippians 2:15
so that you may be blameless and pure, children of God without fault in a crooked and perverse generation, in which you shine as lights in the world

Revelation 1:20
This is the mystery of the seven stars you saw in My right hand and of the seven golden lampstands: The seven stars are the angels of the seven churches, and the seven lampstands are the seven churches.

Revelation 2:5
Therefore, keep in mind how far you have fallen. Repent and perform the deeds you did at first. But if you do not repent, I will come to you and remove your lampstand from its place.