Leviticus 2:13 "Neither shall you omit salt the covenant of your G‑d"

All sacrifices must be offered with salt (see Positive Mitzvah 62). We are not allowed to present a sacrifice or meal offering which does not contain salt.

The Torah calls the addition of salt to the sacrifice "the covenant of your G‑d."

A covenant is a treaty or pact made between two parties.

The Torah uses salt to symbolize HaShem's covenant with the Jewish people.

Salt does not spoil and it retains taste for a very long time, so, too, HaShem's bond with the Jewish people will never be broken.