Ye are the light of the world. A city that is set on an hill cannot be hid. Ye are the light of the world - That is, the instruments which God chooses to make use of to illuminate the minds of men; as he uses the sun (to which probably he pointed) to enlighten the world. Light of the world, נר עולם ner olam, was a title applied to the most eminent rabbins. Christ transfers the title from these, and gives it to his own disciples, who, by the doctrines that he taught them, were to be the means of diffusing the light of life throughout the universe.
A city that is set on a hill - This place may receive light from the following passage in Maundrell's Travels. "A few points toward the north (of Tabor) appears that which they call the Mount of Beatitudes, a small rising, from which our blessed Savior delivered his sermon in the fifth, sixth, and seventh Chapter s of Matthew. (See the note on Matthew 5:5). Not far from this little hill is the city Saphet, supposed to be the ancient Bethulia. It stands upon a very eminent and conspicuous mountain, and is Seen Far and Near. May we not suppose that Christ alludes to this city, in these words of his, A city set on a hill cannot be hid?" p. 115. Quesnell remarks here: "The Christian life is something very high and sublime, to which we cannot arrive without pains: while it withdraws us from the earth, and carries us nearer heaven, it places us in view, and as a mark, to the malice of carnal men."