Jesus paid the price for our redemption, but it is not for sale. It is given to anyone who will accept it by faith. It is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men. Christians are to flavor the life-styles of communities in which they live. The life-style of Christians is to make life itself more palatable and desirable.
Salt is a preservative.
Paul point to specific subjects for thought that build our relations with others and with Jesus Christ. Following the Apostle's words to the Philippians, we find in them a recipe for better Christian unity and fellowship.