"Hermetically sealed"

I heard the phrase recently and didn't understand how it could be connected to the Greek god Hermes.

Hermes Trismegistus... is the purported author of the Hermetic Corpus, a series of sacred texts that are the basis of Hermeticism... During the Middle Ages and the Renaissance, the writings attributed to Hermes Trismegistus, known as Hermetica, enjoyed great prestige and were popular among alchemists. The "hermetic tradition" consequently refers to alchemy, magic, astrology and related subjects. The texts are usually divided into two categories: the "philosophical", and the "technical" hermetica. The former deals mainly with issues of philosophy, and the latter with practical magic, potions and alchemy. Spells to magically protect objects, for example, are the origin of the expression "Hermetically sealed". 

And of interest:

Hermes Trismegistus has a major place in Islamic tradition. He writes, "Hermes Trismegistus is mentioned in the Qur'an in verse 19:56-57:"Mention, in the Book, Idris, that he was truthful, a prophet. We took him up to a high place"...

Hermes Trismegistus is identified as Idris (prophet) the infallible Prophet who traveled to outer space from Egypt, to heaven, where Adam and the Black Stone he brought with him when he landed on earth in India, originated. According to ancient Arab genealogists, Muhammad the Prophet, who also is believed to have traveled to outer space on the night of Isra and Mi'raj to the heavens is a direct lineal descendant of Hermes Trismegistus...

And, for the English majors -

In the novel The Life and Opinions of Tristram Shandy, Gentleman by Laurence Sterne the narrator's father wishes to call his newborn son Trismegistus (after Hermes Trismegistus) because he considers the name particularly auspicious. Unfortunately, his wife's maid bungles the pronunciation of the name and the child is instead baptised Tristram, a name the father particularly despises.