Today, Jesus speaks about three images that are simple and evident for everyone: salt, light and a city. Jesus indicates what a disciple is and what a disciple should be. All three have something in common. Salt doesn't exist for itself, but as a condiment. Light doesn't exist for itself but to shine. The city on the top of a hill is there to be visible and so to give directions. The value of all three is to give something to others. A disciple exists for others, to share their own existence.
The first reading tells us what a true disciple has to share: bread for the hungry, shelter for the homeless, clothes for the naked. I would extend this list by adding the sharing of our time, helping in different ways, sharing our experiences with others and volunteering wherever we see a need. These are the things that are already happening among many of us.
There is a danger. People can see our good works and say: how nice, how generous, how great you are. Sometimes, when people appreciate me for something, I am a bit proud (me stupid!) but also a bit sad (thanks to God). Sad because whatever I am able to do or to give, is there because I have received so much from Christ before, but people often don't see this. They see what I do but they don't realise that I give what I give because I am privileged, because Christ has given me so much. "Hallowed THY name, THY will be done" we say in Our Father. They should thank not just me, but God.
This is what the second reading stresses. Saint Paul emphasises that all that he offers is about Christ, about the power of God.
So a true disciple shares not out of generosity, but out of gratitude. And the one who shines is Christ and then others can discover God.