Adam Clarke on Psalms 88:12

The land of forgetfulness? - The place of separate spirits, or the invisible world. The heathens had some notion of this state. They feigned a river in the invisible world, called Lethe, Ληθη, which signifies oblivion, and that those who drank of it remembered no more any thing relative to their former state. - Animae, quibus altera fato

Corpora debentur, lethaei ad fluminis undam

Securos latices et longa oblivia potant.

Virg. Aen. 6: 713.

To all those souls who round the river wait

New mortal bodies are decreed by fate;

To yon dark stream the gliding ghosts repair,

And quaff deep draughts of long oblivion there.