Lev 2-3; Jn 21; Pr 18; Col 1

Leviticus 2:13 Moreover, you must season every one of your grain offerings with salt; you must not allow the salt of the covenant of your God to be missing from your grain offering—on every one of your grain offerings you must present salt.

"Covenant of Salt" - most commentators agree that salt refers to sureness and legal nature of the transaction (https://www.gotquestions.org/salt-covenant.html)