Try this interpretation of what it means for Christians to be salt.
I suggest that being salty as a Christian means at root being so profoundly satisfied by Christ as our eternal reward, we are freed from fear and greed for the sacrifices of love, while rejoicing at persecution.
Let’s see if that works in three texts.
Read Matthew 5:11-13
The immediate context of “You are the salt of the earth” is “Blessed are you when you are persecuted . . . Rejoice and be glad . . . because your reward is great in heaven.” When someone lives like this, it is so utterly unnatural and amazing and wonderful, it tastes really good. Joyful suffering for the sake of Christ is startling, spectacular, salty.
Read Mark 9:47–50
Jesus moves from the fire of hell to saying “Everyone will be salted with fire.” I take that to mean, everyone will encounter fires of trouble and pain in life, and this experience can make you salty. It salts you. In other words, close calls with eternity, where you can smell the flames of hell and the scents of paradise can fill you with an amazing dissatisfaction with this world and a profound satisfaction in Christ as your eternal reward.
Verse 50a says this is good, and if you lose it, you may never get it back. Then verse 50b says, “Have salt in yourselves and be at peace with each other.” Few things make for greater peace than freedom from the need for this world’s affirmation and rewards. Such people don’t return evil for evil. They rejoice when reviled. They are peacemakers. And that freedom for love comes from the salt of satisfaction in the reward of Jesus now and in the age to come.
Read Colossians 4:6
The question here is: How does being seasoned with salt help us “know how to answer each person”? How does being salty make you more discerning? Answer: If we are deeply satisfied with Jesus as our reward, and freed from the cravings for approval and for reward on earth, then our faculties of discernment about what is loving, will be less clouded with selfish distortions. We will “know” more readily what love calls for, because we will be more ready to love.
This is my suggestion: to be the salt of the earth and the light of the world means that at root Christians are so profoundly satisfied by Christ as our eternal reward, we are freed from fear and greed for the sacrifices of love, and are able to rejoice at persecution. When the world sees this, they see the glory of Christ and taste the satisfying pleasure of who he is.