Lethe was also the name of the personification of forgetfulness and oblivion, with whom the river was often associated.

In Greek mythology, Lethe /ˈliːθi/ (Greek: Λήθη, Lḗthē; Ancient Greek:)  was one of the five rivers of the underworld of Hades.

Isaiah 28:15:

Because ye have said, We have made a covenant with death, and with hell are we at agreement; when the overflowing scourge shall pass through, it shall not come unto us: for we have made lies our refuge, and under falsehood have we hid ourselves:

Also known as the Ameles potamos (river of unmindfulness), the Lethe flowed around the cave of Hypnos and through the Underworld, where all those who drank from it experienced complete forgetfulness.

Lethe was also the name of the Greek spirit of forgetfulness and oblivion, with whom the river was often identified.

In Classical Greek, the word lethe literally means “oblivion”, “forgetfulness”, or “concealment”.

According to Statius, it bordered Elysium, the final resting place of the virtuous. Ovid wrote that the river flowed through the cave of Hypnos, god of sleep, where its murmuring would induce drowsiness.

The shades of the dead in the underworld were required to drink the waters of the Lethe in order to forget their earthly life.

In the Aeneid, Virgil writes that it is only when the dead have had their memories erased by the Lethe that they may be reincarnated.

Some ancient Greeks believed that souls were made to drink from the river before being reincarnated, so they would not remember their past lives.

Other commentary says:

When the wicked or evil deceased souls drink from the river of forgetfulness, their memory of who they are is erased, they enter into a state of being hypnotized, so that they may not retain memory of who they are, where they come from, why they existed etc.

And finally they also forget that they are an extension of God.

And when they forget that they are an extension of God, they then take on another evil nature of not regretting, neither wanting to repent of the evil deeds they committed, they curse, use profanity,etc.

As they are tortured by the tormentors; instead of repenting, they just increase in speaking words of profanity, vulgar, F*** word, which just amplifies and empowers their tormentors to continue to torment them.

That same negative influence you can observe it among those that behave wickedly on the Earth…

2 Peter 2:10 (NKJV)

¹⁰ and especially those who walk according to the flesh in the lust of uncleanness and despise authority. 

They are presumptuous, self-willed. They are not afraid to speak evil of dignitaries,

The Myth of Er in Book X of Plato’s Republic tells of the dead arriving at a barren waste called the “plain of Lethe”, through which the river Ameles (“careless”) runs.

“Of this they were all obliged to drink a certain quantity,” Plato wrote, “and those who were not saved by wisdom drank more than was necessary; and each one as he drank forgot all things.”

A few mystery religions taught the existence of another river, the Mnemosyne; those who drank from the Mnemosyne would remember everything and attain omniscience.