The table itself is, as always, a reminder of the altar in the Temple, for eating could and should become an act of sacrifice.
In other words, the relation, between man and the food he consumes, as expressed in the intention behind the eating of the food, corresponds to the cosmic connection between the material and the spiritual as expressed by every sacrifice on an altar.
Especially is this true on the Sabbath, when the Sabbath feast takes on the character of a sacramental act, a sort of communion, in the performance of the mitzvah of union of the soul, the body, the food, and the essence of holiness.
Therefore at mealtimes the table always has on it a salt container, just as salt had to be on the holy altar as a sign of the covenant of salt.
–Rabbi Adin Steinsaltz
From "An additional note on the Kiddush ritual" in The Thirteen Petalled Rose by Rabbi Adin Steinsaltz