The Greek verb halizō (ἁλίζω) means to salt or season with salt — derived from halas (G217, salt). In the ancient world, salt preserved, purified, and consecrated. To salt something was to mark it as set apart.
Jesus declares His disciples to be the salt of the earth (Matthew 5:13). Salt preserves from corruption and gives flavor — so believers preserve moral integrity and bring the flavor of the kingdom into ordinary life. Salt also seals covenants (Numbers 18:19). Saltless disciples are useless. Paul's call to let speech be seasoned with salt (Colossians 4:6) demands both grace and substance.