Because Salt was created on the second Day. Because Salt has the power to alter whatever it touches. Salt represents stability between opposing forces as in fire and water. When these waters were separated the lower waters protested that they desired to be close to Hashem like the upper waters were. As a result G-d established the Covenant of Salt.
Salt is the product of an alliance between fire from the sun and ocean water.
The fire from the sun bears down upon the water. When man was created by G-d, man was formed from the dust of the ground. It is spelled Aleph Yud Shin. Both Eesh and Ee Shaw constitute the letters Aleph Shin which represents Aysh meaning fire. Next we observe the earth from which Adam was formed which is representative of Adam's Mother.