The two images found in today's Gospel (Matthew 5:13-16) are very powerful ones. And the would have been very important for the disciples and others at the time of the Lord.
I sometimes watch different food shows on TV and am always fascinated by the different recipes they show. One thing theat all the expert chefs try and communicate is that salt enhances other flavors. It only takes a little to elevate the intensity of the food, allowing the natural flavor to come out in a more satisfying way. By referring to his disciples (and, by extension, us) as salt, Jesus wanted to show the importance of mixing in with the rest of the world. If humans are good, created in the image and likeness of God, then we, when we live our faith, can only enhance what is already there. Our presence, interacting with others, can allow the true nature of people to come forth in a more intense way. But, just as the Lord warned, if we just sit there and are not "mixing it up" with others, we can go flat, lose or ability to enhance people and situations, and be "no longer good for anything". I see this as a powerful message, and a warning. We better make sure we live our faith in our interactions with others, or else we may lose it.
Light is the other image given by the Lord today. And His warning is a clear one. Light cannot be hidden. It must be used to illuminate everyone around. He would often return to this image of light, frequently contrasting it with darkness. In days when people did not have multiple light sources, the light in each household was important and precious. All in the house needed it in order to complete the tasks of the day. If anyone blocked the light, others would suffer. So too in our relationships. If we do not bring the light of Christ into the situation, allowing our faith to illuminate the various situations, how can we hope to finish what has to be done?
One thing that is clear in both of these images is that we have to work at it in order to follow the teaching of Christ. We cannot just sit back and think "I believe, so I am OK." Salt must be infused into the mixture of life. Light must illuminate every dark part of life. This is how life can reach its potential. This is how we, as followers of the Lord, assist in the mission. How can we be what we are called to be today - salt and light?