Why was salt so important to Gandhi?

Answer 1

The British had imposed salt tax.

Mahatma Gandhi wanted to highlight the injustice of British Rule. Salt was a item of common use, a very basic item. The Mahatma realized that by highlighting the fact the something as basic as salt was taxed by a foreign power, he would be able to stir the common masses.

Taxing salt is something like imposing tax on air. A just power, a just ruler would never do it. Mahatma wanted to highlight the fact that the British rule was inherently unjust. It not only looted the country but also taxed even the very basic requirement of an individual.

Such was his understanding and his connect with the common masses, that Gandhi's Salt Satyagraha mobilized the entire country.