Christians are to model selflessness before the world. We are to be a pattern for others to follow instead of aping the silly selfishness of the world. Its primary manifestation is seen in the Christian's relationship with God. Next in importance is the Christian's relationship with his brethren. First, Christians are to be at peace with one another.
Christians are the seasoning and preservative of society.
Clearly one way to retain savory saltiness is to be at peace with the brethren. This is accomplished first through humility. Do not set your mind on high things. Like mindedness grows out of mutual association. It comes from humility of heart which is not wise in its own opinion.