We had a church away day last weekend and one of the passages looked at was from the sermon on the mount - salt and light. The speaker didn't (to my mind) really explore much about light - much of it was merely assumed as known or associated with witnessing. What might Matthew/Jesus have meant here by "light" I wonder? It is a metaphor capable of various meanings depending on where you look. It could be talking about standing out. It could be one part of an ethical dualism (Greek thought?) of light and dark as good and bad. It could be taking some of the Ancient Near Eastern imagery associated with light and deity found also in the OT (e.g. Isaiah 60:1-3; Isaiah 49:6; Numbers 6:24-26, etc.) that spoke of blessing, salvation and the presence of God. Given that Matthew so often wants to show OT fulfilment, perhaps some of this is implied here. But in what sense are we "light" in terms of blessing/salvation/God's presence if this is indeed what is being said?
Perhaps there is a clue in the way that the servant imagery of Isaiah is applicable both to an individual and also to God's people more broadly. Maybe it also has links to the idea of being blessed and a blessing to others as promised to Abraham. What I wonder is, how much of this cluster of imagery is applicable in this instance - particularly the "salvation" bit. We tend to like to only use such language of what Jesus did and does, not of ourselves. But is there a sense in which derivatively God's people are "light" in the sense of salvation to the world also? Or, are we only mirrors who reflect the true light to others?