In conclusion, Jesus compared a disciple to salt. Salt was important in the ancient East because it flavored food, retarded decay, and in small doses fertilized land. [1] All of these uses are in view in this passage. Most salt in the ancient world came from salt marshes or the like rather than from the evaporation of salt water, so it contained many impurities. The sodium was more soluble than many of the impurities. It could leach out leaving a substance so dilute that it was of little worth. [2][source]
Just as a disciple can cease to follow Jesus, so salt can lose its saltiness. In that case both things become useless. What distinguishes a disciple of Jesus from a non-disciple, what makes him or her "salty," is his or her allegiance to Jesus (cf. Matthew 5:13; Mark 9:50). Farmers added salt to animal dung to slow down the fermentation process so they could preserve it as fertilizer until they needed to use it. [3] The disciple who does not continue following Jesus faithfully falls under divine judgment, not that he will lose his salvation, but part of his reward, specifically the opportunity for further significant service. [source][source][source]
Jesus urged His hearers to listen carefully to what He had said (cf. Luke 8:8). Prospective disciples need to realize the implications of following Jesus and then choose to follow Him faithfully. [source][source][source]
"His [4] main point is that successful discipleship requires Jesus to be a priority in life." [5][source]