http://revach.net/article.php?id=3572

Section: Parshas HaShavua   Category: Quick Vort
Parshas Vayikra: Rav Yaakov Kaminetzky - Salt, The Lowest Of The Low
Rashi says that the reason we put salt on every korban is because Hashem promised the lower earthly waters from the time of creation when they were split from the upper waters that they will be brought on the Mizbei'ach.  "Therefore," Rashi says, "we do Nisuch HaMayim, the pouring of the water on Succos, and salt on the Korbanos."  (Vayikra 2:13)  The Maharal MiPrague asks, "why bring salt?  Why not perform Nisuch HaMayim, compensating the water itself with every korban that goes up?"

Rav Yaakov Kaminetzky answers that bringing salt was the greatest compensation for the lower waters.  The lower waters felt that spirituality is measured by lofty heights, and the upper waters which were in the heavens, were far more fortunate.  Hashem wanted to show the water that even the physically low, can reach lofty heights.  For this reason we bring salt.  To make salt, we evaporate the water which rise towards the heavens.  The lowly salt remains behind firmly anchored to the earth.  Hashem says, "It is the salt, the lowest element of the lower waters that should be brought on the mizbei'ach as it too can reach great spiritual heights."