Jesus uses these two metaphors —“salt and light”—to refer to his listeners who take to heart his teaching on the Beatitudes. We can add “earth and world” as metaphors referring to the people who are destined to go to heaven.

In those days, salt was used not just for giving taste to food, but for kindling fire along with dry dung, used for cooking. This may answer our question, “Can salt lose its taste?” “Can it be thrown out and trampled underfoot?” The answer is Yes, in this sense.

Light was powered by olive oil. We may run out of oil. But by the fact that we are Christians, we cannot afford to run out of it. We have unlimited supply from Jesus. Lives of the saints and our holy lives serve as light to the next generations of believers.

In giving service to the brethren, we, Christians, should not lose steam. We should never conk out, like machines. We must serve the Kingdom of God until the end of our lives.

We can take the “earth and the world” metaphorically to mean the Christian communities or the secular world in need of sound teachings and directions.

The brook near where Elijah was hiding ran dry, because no rain had fallen in the land. So the Lord said to Elijah: “Move on to Zarephath of Sidon and stay there. I have designated a widow there to provide for you.” He left and went to Zarephath. As he arrived at the entrance of the city, a widow was gathering sticks there; he called out to her, “Please bring me a small cupful of water to drink.” She left to get it, and he called out after her, “Please bring along a bit of bread.” She answered, “As the Lord, your God, lives, I have nothing baked; there is only a handful of flour in my jar and a little oil in my jug. Just now I was collecting a couple of sticks, to go in and prepare something for myself and my son; when we have eaten it, we shall die.” Elijah said to her, “Do not be afraid. Go and do as you propose. But first make me a little cake and bring it to me. Then you can prepare something for yourself and your son. For the Lord, the God of Israel, says, ‘The jar of flour shall not go empty, nor the jug of oil run dry, until the day when the Lord sends rain upon the earth.’” She left and did as Elijah had said. She was able to eat for a year, and Elijah and her son as well; the jar of flour did not go empty, nor the jug of oil run dry, as the Lord had foretold through Elijah.

Jesus said to his disciples: “You are the salt of the earth. But if salt loses its taste, with what can it be seasoned? It is no longer good for anything but to be thrown out and trampled underfoot. You are the light of the world. A city set on a mountain cannot be hidden. Nor do they light a lamp and then put it under a bushel basket; it is set on a lampstand, where it gives light to all in the house. Just so, your light must shine before others, that they may see your good deeds and glorify your heavenly Father.”