Kosher explained vividly

To Jews the body is the soul’s house, so we take extra care of what we put in it.
A healthy body gives us the strength to fulfil the mitzvot and sacred actions of our religion.
By keeping ourselves healthy and Kosher we take responsibility for and demonstrate our deep appreciation to G-d for the most precious divine receptacle entrusted to us – our body.
This is, in essence, what Kosher means.