“Salt therefore is good, but if even the salt has lost its savour (literally ‘if it become foolish'), with what shall it be seasoned. It is fit neither for the land nor for the dunghill. Men cast it out.”
Jesus then finishes with a warning of the danger of becoming a disciple and then losing the very ‘virtue' which makes us useful in His service, our totally dedicated hearts. He does it in terms of salt. Salt is good. It offers great benefits to man while it retains its saltness. It can be used to season food. It can preserve food. It is offered as a an essential part of sacrifices. There is evidence that in some forms (as salty earth) it can fertilise the ground (this is certainly known in modern Egypt). It can kill weeds, although care must be taken not to contaminate the ground. It can prevent dunghills from fermenting too quickly so that they can be preserved for later use. But in all cases only if it retains its saltness.
In order to understand this idea of losing is saltness we have to recognise what the Palestinian meant by ‘salt'. The word was used of what was gathered from the shores of the Dead Sea, or obtained by evaporation from it, the crystals of which included both what we call salt, and carnallite. It would then be stored as ‘salt'. In some cases the salt content might be dissolved away and this would leave the savourless carnallite which they would still have described unscientifically as ‘salt'. Thus when they came to their store of ‘salt' they discovered that it had lost its savour and was useless. So they ‘threw it away'. And, says Jesus, professing Christians who have lost their savour may just as well be thrown away, as they will be at the Judgment.
‘Lost its savour.' The word used here means literally that it had ‘become foolish. The parable is being half applied. It is foolish men, men who do not trust God, who lose their savour. In Mark 9:50 the salt is described as more literally having ‘lost its saltness'. It has been suggested that this is a matter of translation from the Aramaic tradition, and that both are in their own way correct. In Hebrew (and therefore probably in Aramaic) the root ‘tpl' can mean ‘saltlessness' (tapel - Job 1:6) and ‘folly' (tiplah - Jeremiah 23:13; Job 1:22; Job 24:12). Thus Mark or his source can be seen as having translated in one way, Luke or his source as having translated in the other (Semitic languages had no vowels and thus either meaning to tpl is possible).