"You should season every one of your meal-offering sacrifices with salt. You should not leave out the salt .... You should offer salt on all your (burnt) offerings....." [Vayikra 2:13]
According to chassidic thought, offering a sacrifice on the Altar is a process of offering up one's animal soul - the source of all physical desires - to G-d.
Since these desires come primarily from the blood, every sacrifice must be salted to signify the strong resolution of the person bringing the sacrifice to extract those desires from the animal soul, like salt that extracts blood.
[Based on Ohr Hatorah, Vayikra]