Jesus ended His words on counting the cost with a warning. He had just said that whoever does not forsake all "cannot be my disciple" (Luke 14:33). Salt is valued for its flavor; salt without savour has lost the very thing that makes it salt. The question asks what could possibly restore it, and the expected answer is: nothing. Barnes applies it to people: "Real piety, true religion, is of vast value in the world," but "a mere profession of religion is fit for nothing."

Jesus answers His own question in the next verse: "It is neither fit for the land, nor yet for the dunghill; but men cast it out" (Luke 14:35). Then He closes with a call: "He that hath ears to hear, let him hear" (Luke 14:35).

The verb behind "have lost his savour" is moraino. Thayer explains that in the Bible it can mean "to make flat and tasteless." The same verb is used in Romans 1:22, where people professing to be wise "became fools."

The phrase "wherewith shall it be seasoned?" reads literally "with what will it be seasoned?" Salt was the thing used to season other things, so if salt itself goes flat, there is nothing left to season it with.

Jesus used this picture more than once. In the Sermon on the Mount He told His disciples, "Ye are the salt of the earth" (Matthew 5:13), and Barnes points readers there. In Luke, the saying closes a hard teaching about cost, so the warning is about a following of Jesus that keeps the name but loses the substance. Barnes says all such professors are "fit only to be cast out and rejected."

Gill notes on Luke 14:35 that salt which has "lost its savour and spirit" is "entirely useless." The sobering point is meant to stir the hearers, not to crush them. Jesus ends with an invitation to listen: "He that hath ears to hear, let him hear" (Luke 14:35).