Yahweh’s parable about the cedar continues.
Here “threw it down to Sheol” is an idiom that means to kill. “The pit” refers to the grave; because the grave was thought to be the entrance to the world of the dead, the pit also represents that world. See how you translated this in Ezekiel 31:14. AT: “when I killed the cedar and it went to Sheol with everyone else that is dead” (See: rc://en/ta/man/translate/figs-idiom and rc://en/ta/man/translate/figs-metonymy)
“that were already deep down in the ground.” This is an idiom. AT: “that had already died and are now in Sheol” (See: rc://en/ta/man/translate/figs-idiom)
“the best trees of Lebanon that everyone would want; trees that got a lot of water.” This is describing the trees of Eden that were in the lowest parts of the earth.
This is something that everyone would want because it is very good.