In Jeremiah 2:14, this signifies people who think not from themselves, but from others. (Apocalypse Explained 836)

In Revelation 13:16, this signifies people who are wise from others. (Apocalypse Revealed 604)

To be in a state of slavery is to be under the domination of evil spirits. (Arcana Coelestia 892)

'A slave' means people who do not think for themselves but from others.