Salt is good
To make meat savoury, and keep flesh from corrupting; and so is the grace of God, to season men's hearts, make their discourse savoury, and preserve them from the corruption of sin: and so men made partakers of the grace of God; they are good and useful to others, both by their words and actions, and especially ministers of the Gospel, who are "the salt of the earth", (See Gill on Matthew 5:13); and here Christ may chiefly intend his apostles:
but if the salt hath lost its saltness, wherewith will ye season it?
there is no recovering it, it becomes good for nothing; (See Gill on Matthew 5:13);
have salt in yourselves;
the doctrine of grace, and word of Christ, prudence in talk and conversation, and holiness of heart and life, so as to behave wisely towards them that are without;
and have peace one with another;
which the God of peace calls unto, the Gospel of peace requires, and the grace of God teaches. Salt is an emblem of firm union, concord, and agreement: hence the covenant of peace is called a covenant of salt, ( Numbers 18:19 ) , compared with ( Numbers 25:12 ) . This exhortation, very appropriately follows upon the making mention of salt in different senses; especially, this exhortation was the more necessary to the disciples at this time, since they had been very lately warmly disputing the point among themselves, who should be greatest in the kingdom of the Messiah; and which had occasioned this discourse of Christ's.