guiding light

Matthew 5:13-16

Jesus uses two analogies to describe the character of citizens of the kingdom of heaven. This is consistent with his teaching style through out his ministry: using parables, comparisons, analogies to make a point.
The two descriptions that Jesus uses here are salt and light. We don't use salt in the same way they did in the ancient world and we don't value salt the same way. I think Jesus was probably referring to the preservative nature of salt and possibly the subversive nature of salt. When salt is used in food properly it enhances the flavours of what is already there and you don't really notice it. This would be a good description of the citizen of the kingdom - sometimes going unnoticed but missed when not there.
In term of light, the whole purpose of the light is to show the way. Jesus makes it clear the the life of the citizen of the kingdom is to show the way to God: let our good deeds shine so others see them and give glory to God. In the context, Jesus is talking specifically about the way that we endure opposition, hardship and persecution (v. 10-11). We rejoice in the midst of persecution without seeking vengeance and without flinching and people will realize that there must be something to what we believe. This has certainly been proven through out history.
I know that I act like a child when I face hardship or opposition: I lash back, I throw a tantrum, I scream and swear. Sure, I might be outwardly composed but if you could see me when I'm alone or if you could look into my mind at that moment it wouldn't be pretty. God, please let me be your light and salt in this world. Let my life shine is such a way that it points to you and brings you glory from others.