serpent on a pole

OK, I may be showing my ignorance here but I wasn't entirely clear about the reference to the 'brazen serpent on a pole' in the hymn I've just quoted. For the record, it's a reference to the story in Numbers 21, 8-9, where God tells Moses how to protect the people from serpents:

And the LORD said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live.
And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived.

There is a reference to this passage in John 3, 13-14, where the serpent on the pole is identified with Christ on the cross. It is the sequence where Jesus speaks with Nicodemus, the Pharisee:

And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up:
That whosoever believeth in him should not perish, but have eternal life.

So the hymn that I quoted alludes to two exilic experiences, one Jewish - the wandering of the Israelites in the wilderness - and one Greek - Eurydice's exile in the underworld. This makes me think of Levinas and Derrida, but let's not go there this morning :o)