Al-Bzzar narrated that the Prophet (peace be upon him) said: "You will soon be to the people what the salt represents to food, and the food's flavor dosen't become favorable unless there is salt in it."
Al-Baghawi said in his commentary on the Qur'an that Abdullah bin Umar (may Allah be pleased with him) related from the Prophet (peace be upon him) that he said: "There are four blessings that Allah has sent down to the earth from the heavens: iron, fire, water and salt." This Hadith should only be rlated from Ibn Umar (RA).
Salt is favorable for people's bodies and food. Further, salt is favorable and beneficial when blended with any substance, including gold and silver, as it makes gold more yellowish and whitens silver. Salt decomposes, cleanses, dries the thick humidity, strenghtens and purifies the body and helps against open mangy sores.
When used as eyeliner salt, especially gem salt, will remove the excess fat or flesh and the yellowish color from the eye. Salt also prevents malignant infections from spreading, works as a laxative and helps against pleurisy when the stomach is anointed with it. Salt cleanses the teeth, prevents them from decaying, and strenthens the gums and makes them firm. There are many other benefits for the salt.
Taken From: Healing With The Medicine Of The Prophet (peace be upon him), by Imam Ibn Qayyim Al-Jauziyah