NOTES for Mat 5:13-26
The first property of salt that comes to mind, the salt with which Christ compared His disciples, is its ability to keep any substance from decay, the companion of death. We also know that only a very small amount of salt is needed to change the taste of a large portion of food, which means that even while remaining a minority, Christians can have a positive effect on the whole world. But the point is not only in these qualities of salt, which have not changed over the centuries: the listeners to the Sermon on the Mount knew and observed ancient customs connected with salt. Salt was a symbol of faithfulness; sharing salt together sealed an alliance more firmly than an oath and was a sign of unbreakable friendship. This means that Christ's disciples too are called to be such bearers of truth and reconciliation in a world torn apart by hostility.
He also called the disciples the light of the world, and this is striking, because another time He called Himself that (John 8:12, 9:5). Here is one of the first indications of the height to which He wants to raise those who trusted Him and followed Him. Yes, He came not to trample us into the dirt by His greatness, but to pull us out of the dirt and cleanse us.
And naturally, though for many people still unexpectedly, He begins to emphasize how His actions correspond to the law. Today many find it hard to connect what Christ brought into the world with the provisions of Old Testament law. But what seemed to some people to be a novelty was revealing precisely what had been laid down from ancient times.
Speaking about the need to surpass the righteousness of the scribes and Pharisees, Jesus reveals that the motivation of actions, and the condition of soul that dictates them, are no less important than the actions themselves. If hatred leads to murder, then hatred is already the beginning of murder. And however important it is to cut down a poisonous tree that has grown large, it is even more important to keep it from taking root.