Halas (G217) is salt. In the ancient world, salt was precious — worth its weight in trade, used to preserve food, seal covenants (Numbers 18:19; 2 Chronicles 13:5), and purify offerings. Jesus calls his disciples 'the salt of the earth' (Matthew 5:13). Paul urges speech 'seasoned with salt' (Colossians 4:6). Mark 9:49–50 contains a challenging cluster of salt sayings.
Salt as covenant symbol runs through both Testaments. A 'covenant of salt' is permanent and unbreakable. When Jesus calls disciples 'the salt of the earth,' he is calling them to be covenant-keeping, preserving, purifying agents in a decaying world. Saltless salt is a contradiction — a disciple without distinctive witness has lost their very nature. Paul's 'speech seasoned with salt' means gracious yet truthful, tasty and purifying.